Aqueous ink composition and method of manufacturing the same

ABSTRACT

An aqueous ink composition comprising: a pigment, having a particle diameter as determined by the light scattering method of no less than 20 nm and no more than 200 nm; and a water dispersible polymer, having a styrene-equivalent number average molecular weight of as determined by gel permeation chromatography no less than 5000 and no more than 200000, having a surface tension of no less than 20 mN/m and no more than 40 mN/m, and wherein the abovementioned pigment is a polymer-coated pigment that is coated with the abovementioned water dispersible polymer, is provided. The water-dispersible polymer may be a copolymer of monomers, mainly comprising acrylic acid and/or methacrylic acid and an acrylate and/or methacrylate. With this ink composition, the printing quality can be improved.

RELATED APPLICATION INFORMATION

The present application is a Divisional of U.S. patent application Ser.No. 11/906,119, filed Sep. 28, 2007, which is a Continuation of U.S.patent application Ser. No. 10/819,096, filed Apr. 6, 2004, now U.S.Pat. No. 7,294,659, issued Nov. 13, 2007, and titled “AQUEOUS INKCOMPOSITION AND METHOD OF MANUFACTURING THE SAME”, and which claimedpriority from Japanese Patents Applications No.: 2003-103473 filed Apr.7, 2003; 2003-173:345 filed Jun. 18, 2003; 2003-359294 filed Oct. 20,2003; 2004-023934 filed Jan. 30, 2004; 2004-036268 filed Feb. 1, 2004;2004-048025 filed Feb. 24, 2004; and 2004-11′1115 filed Apr. 5, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns an aqueous ink composition, a method ofmanufacturing the same, a pigment dispersion polymer of an aqueous inkcomposition for ink jet recording, an ink jet recording method, and anink jet recorded matter.

2. Description of the Prior Art

With prior-art aqueous inks, a surfactant was used as a means fordispersing a pigment in water or a dispersion polymer, having ahydrophobic part and a hydrophilic part, was used for dispersion. Asmethods of coating the surface of a colorant with a polymer, methods ofusing microcapsules, encapsulating a dye ink, as ink jet printer ink,methods of using a polymer-coated dye, wherein a dye is dissolved ordispersed in a water-insoluble solvent and emulsified in water using asurfactant, methods of using encapsulated objects, wherein a sublimatingdispersion dye is dissolved or dispersed in at least one of water, awater-soluble solvent, and polyester, as microcapsules in a recordingfluid, ink compositions comprising colored emulsion-polymerizedparticles and an aqueous material, and methods employing a phaseinversion emulsification reaction or an acid precipitation method havebeen examined. Furthermore, as methods of using components of highrefractive index, methods of providing microparticles of high refractiveindex, formed of an inorganic substance, on the surface of a pigment,etc., have been proposed. Various methods have also been examined inregard to polymer coating.

SUMMARY OF THE INVENTION

Prior-art aqueous inks were unstable in regard to various points. Thatis, firstly, when a surfactant, glycol ether, or other substance havinga hydrophilic part and a hydrophobic exists, adsorption and desorptiontend to occur readily, thus degrading the storage stability. Withordinary aqueous ink, a surfactant, glycol ether, or other substancehaving a hydrophilic part and a hydrophobic part is required to lowerthe blurring of the ink on paper. With an ink that does not use such asubstance, the permeability into paper is inadequate, the types of paperon which uniform printing can be performed are limited, and degradationof the printing quality tends to occur.

Furthermore, when an additive for improving printing quality (acetyleneglycol, acetylene alcohol, silicon-based surfactant di(tri)ethyleneglycol monobutyl ether, (di)propylene glycol monobutyl ether, or1,2-alkylene glycol or a mixture of these) is added to a prior-artdispersion, long-term storage stability cannot be realized, and due topoor redissolution of the ink, the ink tended to clog the nozzle of anink jet head upon drying and attack and thereby lower the adhesionstrength of an adhesive agent and other materials used among thematerials making up the head, thus degrading the discharge stability.Also with a pigment dispersed using such a dispersant, residues of thedispersant remain in the ink system and the dispersant becomes separatedfrom the pigment without contributing adequately to dispersion, causingthe viscosity to become high. When the viscosity becomes high, the addedamount of a pigment or other coloring material becomes restricted andadequate printing quality cannot be obtained, especially on regularpaper.

There is also the issue that, with a pigment dispersed by such adispersant, the residues of the dispersant remain in the ink system andthe dispersant becomes separated from the pigment without contributingadequately to dispersion, causing the viscosity to become high. When theviscosity becomes high, the added amount of a pigment or other coloringmaterial becomes restricted and adequate printing quality cannot beobtained, especially on regular paper. Furthermore in the case where aninorganic substance is used as in Japanese Published Unexamined PatentApplication No. H11-269419, the particles settle under normal usageconditions due to being high in density and the color differs betweenthe initial and end stages of printing.

Furthermore, in cases where the dispersion polymer has styrene as theprincipal component, a high-concentration ink will not have an adequatefixing property on paper or other recording medium and tends to yellowreadily upon long-term storage of a printed matter.

An object of this invention is to provide an aqueous ink composition ofexcellent printing quality. Specifically, an object is to provide anaqueous ink composition with one or both of low blurring and highcoloration properties on regular paper and adequate coloration andfixing properties on specialized paper. Another object of this inventionis to provide an aqueous ink composition suited for ink jet recording,specifically, an aqueous ink composition with at least one of pigmentdispersion stability, discharge stability, and low attacking of anadhesive agent or other material used for making up a head. Yet anotherobject of this invention is to provide an aqueous ink polymer forobtaining such aqueous ink compositions, and an ink jet recording methodand an ink jet recorded matter using such aqueous ink compositions.

The present inventors have completed the following invention uponexamination of the various components of an aqueous ink composition.

The present invention provides an aqueous ink composition comprising: apigment, having a particle diameter as determined by a light scatteringmethod of no less than 20 nm and no more than 200 nm; and a waterdispersible polymer, having a styrene-equivalent number averagemolecular weight as determined by gel permeation chromatography of noless than 5000 and no more than 200000. In addition, the aqueous inkcomposition normally contains water and a water-soluble organiccompound. In this ink composition, the abovementioned particle size ofthe abovementioned pigment is preferably no less than 20 nm and no morethan 150 nm and more preferably no less than 20 nm or 30 nm and no morethan 100 nm. Or, the abovementioned particle size is preferably no lessthan 20 nm and no more than 80 nm. The abovementioned styrene-equivalentnumber average molecular weight is preferably no less than 10000 andmore preferably no less than 20000. This molecular weight is preferablyno more than 100000. Furthermore, the dispersion (Mw/Mn) of theabovementioned styrene-equivalent number average molecular weight ispreferably no less than 2 and no more than 10. Also, the concentrationof the abovementioned pigment is preferably no less than 3 weight % andmore preferably no less than 4 weight %. Also the surface tension ispreferably no less than 20 mN/m and no more than 40 mN/m. With thismode, the pigment is preferably a polymer-coated pigment that is coatedby the abovementioned water dispersible polymer and is preferablyobtained by phase inversion emulsification. Any aqueous ink compositiondescribed above is preferably used for ink jet recording.

In an aqueous ink composition of the invention, as one aspect, the waterdispersible polymer is a copolymer of monomers, mainly comprising acarboxylic-group-containing monomer and an acrylate and/or methacrylate.The carboxylic-group-containing monomer is preferably acrylic acidand/or methacrylic acid. Furthermore, the water dispersible polymer ispreferably a copolymer of monomers having acrylic acid, methacrylicacid, an acrylate, and a methacrylate at a proportion of 80 weight % ormore of the total monomer weight.

In an aqueous ink composition of the invention, as another aspect, thewater dispersible polymer is a copolymer of monomers having benzylacrylate and/or benzyl methacrylate and having these benzyl monomers atan amount of no less than 40 weight % and no more than 80 weight % ofthe total monomer weight.

In an aqueous ink composition of the invention, as another aspect, thewater dispersible polymer is a copolymer of monomers includingparacumylphenoxyethylene glycol acrylate at least in part. In thisaqueous ink composition, the water dispersible polymer is preferably acopolymer of monomers having paracumylphenoxyethylene glycol acrylate atan amount of no less than 50 weight % of the total monomer weight. Thewater dispersible polymer is preferably a copolymer of monomersincluding paracumylphenoxyethylene glycol acrylate, an acrylate otherthan the paracumylphenoxyethylene glycol acrylate, and acrylic acid atleast in part and more preferably at an amount of no less than 80 weight% of the total monomer weight. The acrylate other than theparacumylphenoxyethylene glycol acrylate preferably includes the otheracrylate includes benzyl acrylate and/or butyl acrylate. The preferablerefractive index of said water dispersible polymer is no less than 1.50.

In an aqueous ink composition of the invention, as another aspect, thewater dispersible polymer contains sulfur (S) at an amount of no lessthan 1 weight % and no more than 20 weight % of the total weight of saidpolymer. In the water aqueous ink composition in this aspect, the waterdispersible polymer is preferably a copolymer of monomers mainlycomprising a sulfur-containing monomer, an acrylate, and acrylic acid.Here, the acrylate includes benzyl acrylate and/or butyl acrylate. Thesulfur-containing monomer is preferably a thioacrylate and/or athiomethacrylate, more preferably phenyl thiomethacrylate. In thisaqueous ink composition, the preferable refractive index of said waterdispersible polymer is no less than 1.50.

In an aqueous ink composition of the invention, as another aspect, thewater dispersible polymer is a copolymer of monomers including aurethane acrylate and/or a urethane methacrylate, a non-urethaneacrylate and/or a non-urethane methacrylate, and acarboxylic-group-containing monomer at least in part, the total amountof allophanate bonds and biuret bonds with respect to the polymer solidsis no more than 1.0 mmol/g, and the total amount of urethane bonds, ureabonds, allophanate bonds, and biuret bonds with respect to the polymersolids is no more than 10.0 mmol/g. In the aqueous ink composition inthis aspect, the total amount of allophanate bonds and biuret bonds withrespect to the polymer solids is preferably no more than 0.1 mmol/g.Furthermore, the total amount of urethane bonds, urea bonds, allophanatebonds, and biuret bonds with respect to the polymer solids is no lessthan 0.1 mmol/g. In the aqueous ink composition, the water dispersiblepolymer is preferably a copolymer of monomers having said urethaneacrylate and/or said urethane methacrylate and said non-urethaneacrylate and/or said non-urethane methacrylate at an amount of no lessthan 80 weight % of the total monomer weight. The water dispersiblepolymer is preferably a copolymer of a urethane acrylate, a non-urethaneacrylate, and acrylic acid. The water dispersible polymer is preferablya copolymer having, at least as part of the monomers, benzyl acrylateand/or isobornyl acrylate as the non-urethane acrylate.

In an aqueous ink composition of the invention, as still another aspect,the water dispersible polymer is a copolymer of monomers having aurethane acrylate, a non-urethane acrylate including an alkyl acrylate,a cycloalkyl acrylate, and an aromatic acrylate, and acrylic acid ascopolymer monomers, and having the urethane acrylate and thenon-urethane acrylate at an amount of no less than 80 weight % of thetotal monomer weight, the total amount of urethane bonds, urea bonds,allophanate bonds, and biuret bonds with respect to the polymer solidsis no less than 0.1 mmol/g and no more than 10.0 mmol/g, and the totalamount of allophanate bonds and biuret bonds with respect to the polymersolids is no more than 1.0 mmol/g. The aqueous ink composition in thisaspect may contain glycerin and/or trimethylolpropane.

An aqueous ink composition of the invention, as still another aspect,contains a 1,2-alkyldiol, having 5 to 8 carbons and a monoalkyl ether,with 4 to 10 carbons of an alkylene glycol having no more than 10repeating units. The 1,2-alkyldiol is preferably 1,2-hexanediol and thealkylene glycol monoalkyl ether is preferably di(tri)ethylene glycolmonobutyl ether.

This invention also provides a polymer for dispersion of a pigment inwater, which is used in an ink composition for ink jet recording, thepolymer having a styrene-equivalent number average molecular weight asdetermined by gel permeation chromatography of no less than 5000 and nomore than 200000, being a copolymer of monomers mainly comprising acarboxylic-group-containing monomer and an acrylate and/or methacrylate,and having any of the characteristics (a) through (e) indicated below.

(a) the water dispersible polymer is a copolymer of monomers, havingbenzyl acrylate and/or benzyl methacrylate and having these benzylmonomers at an amount of no less than 40 weight % and no more than 80weight % of the total monomer weight;(b) the water dispersible polymer is a copolymer of monomers, having anacrylate and acrylic acid at an amount of no less than 80 weight % ofthe total monomer weight;(c) the water dispersible polymer is a copolymer of monomers, containingparacumylphenoxyethylene glycol acrylate at least in part;(d) the water dispersible polymer contains sulfur (S) at an amount of noless than 1 weight % and no more than 20 weight % of the total weightthereof,(e) the water dispersible polymer is a polymer of monomers, containing aurethane acrylate and/or a urethane methacrylate, a non-urethaneacrylate and/or a non-urethane methacrylate, and acrylic acid and/ormethacrylic acid at least in part, the total amount of allophanate bondsand biuret bonds with respect to the polymer solids is no more than 1.0mmol/g, and the total amount of urethane bonds, urea bonds, allophanatebonds, and biuret bonds with respect to the polymer solids is no morethan 10.0 mmol/g.

Furthermore, the present invention provides an aqueous ink compositionproduction method comprising: a synthesis step of synthesizing a waterdispersible polymer of any of the abovementioned modes; a pigmentdispersion step of preparing a mixed liquid, containing theabovementioned water dispersible polymer, a pigment, an organic solvent,and water of an excess amount with respect to the abovementioned organicsolvent, and dispersing the abovementioned pigment, with at least a partof the abovementioned polymer coated thereon, in the aqueous phase ofthe abovementioned mixed liquid; and a composition preparation step ofpreparing an aqueous ink composition using the polymer and the pigment,existing in the abovementioned aqueous phase, along with at least a partof the abovementioned aqueous phase or in a state of separation from theabovementioned aqueous phase. The abovementioned synthesis step ispreferably a solution polymerization step and this may be initiated by aradical polymerization initiator.

The present invention also provides an ink jet recording methodcomprising: a step of depositing any of the abovementioned aqueous inkcompositions to a recording medium surface by an ink jet recordingmethod. The present invention also provides an ink jet recorded matterhaving dot patterns, comprising the any of the abovementioned aqueousink composition formed by an ink jet recording method on the surface ofa recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENT

One mode of this invention is an aqueous ink composition comprising: apigment, having a particle diameter as determined by a light scatteringmethod of no less than 20 nm and no more than 200 nm; and a waterdispersible polymer, having a styrene-equivalent number averagemolecular weight as determined by gel permeation chromatography of noless than 5000 and no more than 200000, and another mode is a polymerfor pigment dispersion for ink jet recording. Another mode is an aqueousink manufacturing method, another mode is an ink jet recording method,and yet another mode is an ink jet recorded matter. In the following,the various modes of this invention shall be described in detail. In thepresent Specification, “(meth)acrylic” shall mean both “acrylic” and“methacrylic,” and “(meth)acrylate” shall mean both “acrylate” and“methacrylate.” Also, in this Specification, unless noted otherwise, “%”shall indicate weight % and “parts” shall indicate weight parts.

(Pigment)

The Pigment Contained in this Invention's Aqueous Ink CompositionPreferably has a particle diameter of no less than 20 nm and no morethan 200 nm. With a particle diameter of 20 nm or less, the lightresistance and gas resistance are lowered. When the particle diameterexceeds 200 nm, it becomes hard for gloss to be exhibited on specializedpaper and a difference in gloss with respect to an unprinted part willoccur upon printing. More preferably, the particle diameter is no lessthan 30 nm. The particle diameter is also preferably no more than 150mm, more preferably no more than 100 nm, and even more preferably nomore than 80 nm. In particular, when the particle diameter of thepigment exceeds 80 nm, gloss can be secured on specialized paper evenwhen the concentration of the pigment is high. From the above, theparticle diameter is preferably no less than 20 nm and no more than 80nm, more preferably no less than 20 nm and no more than 70 nm, and evenmore preferably no less than 30 nm and no more than 65 nm. In thepresent Specification, “the particle diameter of a pigment” shall referto the particle diameter of a pigment in a form in which it is notcoated at all. Also, “particle diameter as determined by a lightscattering method” shall refer to the average particle diameter asdetermined by a light scattering method.

An inorganic pigment or an organic pigment may be used as the pigment.As an inorganic pigment, titanium oxide, iron oxide, etc., may be used.Examples of organic pigments that may be used include azo pigments(including azo lakes, insoluble azo pigments, condensed azo pigments,chelated azo pigments, etc.), polycyclic pigments (includingphthalocyanine pigments, perylene pigments, perinone pigments,anthraquinone pigments, quinacridone pigments, dioxan pigments,thioindigo pigments, isoindolinone pigments, quinophthalone pigments,etc.), nitro pigments, nitroso pigments, aniline black, etc.

Examples of pigments for black ink include carbon blacks (C. I. PigmentBlack 7), such as furnace black, lamp black, acetylene black, channelblack, etc., metals, such as copper oxides, iron oxides (C. I. PigmentBlack 11), titanium oxide, etc., and organic pigments, such as anilineblack (C. I. Pigment Black 1), etc. A carbon black, which iscomparatively low in specific density and does not settle readily inwater, is preferable for ink jet printing.

Furthermore, for color inks, C. I. Pigment Yellow 1 (Fast Yellow G), 3,12 (Dis-Azo Yellow AAA), 13, 14, 17, 24, 34, 35, 37, 42 (Yellow IronOxide), 53, 55, 74, 81, 83 (Dis-Azo Yellow HR), 93, 94, 95, 97, 98, 100,101, 104, 108, 109, 110, 117, 120, 128, 138, 153, and 180, C. I. PigmentRed 1, 2, 3, 5, 17, 22 (Brilliant Fast Scarlet), 23, 31, 38, 48:2(Permanent Red 2B (Ba)), 48:1 (Permanent Red 2B (Ca)), 48:3 (PermanentRed 2B (Sr)), 48:4 (Permanent Red 2B (Mn)), 49:1, 52:2, 53:1, 57:1(Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81 (Rhodamine 6G Lake),83, 88, 101 (Red Iron Oxide), 104, 105, 106, 108 (Cadmium Red), 112,114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177,178, 179, 185, 190, 193, 209, and 219, C. I. Pigment Blue 1, 2, 15(Phthalocyanine Blue R), 15:1, 15:2, 15:3 (Phthalocyanine Blue G), 15:4,15:6 (Phthalocyanine Blue E), 16, 17:1, 56, 60, and 63, and C. I.Pigment Green 1, 4, 7, 8, 10, 17, 18, and 36, etc., may be used.However, the pigments are not limited to the above. The content of thepigment in the ink composition is preferably no less than 0.5% and nomore than 30%, more preferably in the range of no less than 1.0%, andeven more preferably in the range of no less than 2%. Yet even morepreferably, the content is no less than 3% and more preferably no lessthan 4%. The upper limit is more preferably no more than 12% and evenmore preferably no more than 8%. With the present ink composition, thepreferable form of the pigment is a polymer-coated pigment. Thepolymer-coated pigment shall be described later.

(Water Dispersible Polymer)

A water dispersible polymer of the present invention preferably has astyrene-equivalent number average molecular weight as determined by gelpermeation chromatography (GPC) of no less than 5000 and no more than200000. Due to the characteristics of a vehicle that is used in usingthe polymer in an ink composition, the polymer will tend to separate andcause adverse effects when the molecular weight thereof is less than5000, that is to be more specific, an adhesive agent, etc., used in ahead will tend to be attacked readily by the separated polymer and anadditive for improving the printing quality, such as an acetylene glycolsurfactant, acetylene alcohol surfactant, silicon-based surfactant, orother surfactant among various types, di(tri)ethylene glycol monobutylether, dipropylene glycol monobutyl ether, or 1,2-alkylene glycol, or amixture of such additives. When the molecular weight exceeds 200000, theviscosity of the ink tends to rise and it becomes difficult to obtain astable dispersion. The molecular weight is more preferably no less than10000 or no less than 20000. The molecular weight is also preferably nomore than 100000.

Also, with a urethane-based water dispersible polymer to be describedlayer, the styrene-equivalent number average molecular weight asdetermined by GPC is preferably no less than 2×10⁴. This is because thedispersion stability of the pigment degrades when the molecular weightis less than 2×10⁴. Also, from the standpoint of dispersion stability ofthe pigment, the molecular weight is preferably no more than 10×10⁴.This is because the dispersion stability of the pigment degradessignificantly when the molecular weight exceeds 10×10⁴. The molecularweight is more preferably no less than 3×10⁴ and even more preferably noless than 5×10⁴ and no more than 8×10⁴. From the standpoint of fixingproperty on glossy paper, the molecular weight is preferably no lessthan 2×10⁴ and no more than 20×10⁴. This is because, the fixing andgloss properties on glossy paper degrade when the molecular weight isless than 2×10⁴ or more than 20×10⁴. The molecular weight is morepreferably no less than 2×10⁴ and even more preferably no less than5×10⁴.

The dispersion of the styrene-equivalent molecular weight (the ratio(Mw/Mn) of the weight average molecular weight (Mw) with respect to thenumber average molecular weight (Mn)) of the present polymer asdetermined by GPC is preferably no less than 2 and no more than 10. Inthis range, dispersion stability can be realized and increase of theviscosity of the ink can be restrained to prevent the dispersion frombecoming unstable. The molecular weight dispersion is more preferably noless than 2 and no more than 4 and even more preferably no less than 2.5and no more than 4.

The water dispersible polymer may be formed of any or two or more typesof various known polymers such as polyacrylic acid esters,styrene-acrylic acid copolymers, polystyrenes, polyesters, polyamides,polyimides, silicon-containing polymers, sulfur-containing polymers,etc. Also, in order to improve the fixing and coloration properties bythe water dispersible polymer, the polymer preferably contains anacryloyl group, methacryloyl group, ethyleneoxy group, propyleneoxygroup, hydroxyl group, amino group, amido group, furan group, thiophenegroup, pyrrolidone group, imidazole group, imidazoline group, lactonegroup, lactam group, carbonate group, epoxy group, urethane group, ureagroup, allophanate group, biuret group, or isocyanurate group, etc.

As the water dispersible polymer for dispersing the pigment, a polymer,using a monomer or oligomer having an acryloyl group, methacryloylgroup, vinyl group or aryl group with a double bond, may be used.Examples of monofunctional monomers that may be used include styrene,(α, 2, 3, or 4)-alkylstyrenes, (α, 2, 3, or 4)-allkoxystyrenes,3,4-dimethylstyrene, α-phenylstyrene, divinylbenzene, vinylnaphthalenes,methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,butyl (meth)acrylate, ethylhexyl (meth)acrylate, other alkyl(meth)acrylates, methoxydiethylene glycol (meth)acrylate,(meth)acrylates of diethylene glycols or polyethylene glycols with anethoxy group, propoxy group, butoxy group, phenoxy group, orparacumylphenoxy group, cyclohexyl (meth)acrylate, benzyl(meth)acrylate, phenoxyethyl (meth)acrylate, isobornyl (meth)acrylate,hydroxyalkyl (meth)acrylates, dimethylamino (meth)acrylate,dimethylaminoethyl (meth)acrylate, dimethylaminopropyl acrylamide,N,N-dimethylaminoethyl acrylate, acryloyl morpholine,N,N-dimethylacrylamide, N-isopropylacrylamide, N,N-diethylacrylamide,other fluorine-containing, chlorine-containing, and sulfur-containing(meth)acrylates, silicon-containing (meth)acrylates, (meth)acrylamide,maleic acid amide, (meth)acrylic acid, etc. For introducing acrosslinked structure, compounds having an acryloyl group ormethacryloyl group, such as (mono, di, tri, tetra, poly)ethylene glycoldi(meth)acrylate, (meth)acrylate of 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,8-octane diol, or 1,10-decanediol, trimethylolpropanetri(meth)acrylate, glycerin (di, tri)(meth)acrylate, di(meth)acrylate ofan ethylene oxide adduct of bisphenol A or F, neopentyl glycoldi(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritolhexa(meth)acrylate, etc., may be used.

The water dispersible polymer preferably has a carboxylic group foradding hydrophilicity. As a carboxylic group in this polymer, acrylicacid, methacrylic acid, crotonic acid, propylacrylic acid,isopropylacrylic acid, itaconic acid, or fumaric acid may be used.ω-carboxy-polycaprolactone monoacrylate, phthalic acid monohydroxyethylacrylate, acrylic acid dimer, etc., may also be used. Just one of thesecarboxylic groups may be used or two or more may be used in combination,and preferably the carboxylic group is acrylic acid and/or methacrylicacid.

The present water dispersible polymer is preferably a copolymer having acarboxylic-group-containing monomer and an acrylate and/or methacrylateas the main components. Also, the proportion of acrylic acid,methacrylic acid, acrylate, and methacrylate with respect to the totalmonomer weight is preferably no less than 80%. If this proportion isless than 80%, good dispersion properties will not be obtained readily.The proportion is more preferably no less than 90% and even morepreferably 100%.

(Benzyl-Group-Containing Water Dispersible Polymer)

The present water dispersible polymer preferably also contains benzylacrylate and/or benzyl methacrylate at a proportion of no less than 40%and no more than 80% with respect to the total monomer weight. If thetotal amount of acrylic monomers and methacrylic monomers that havebenzyl groups is less than 40%, coloration on PPC paper or other regularpaper will be low, and when 80% is exceeded, dispersion stabilitybecomes difficult to achieve. With a benzyl-group-containing waterdispersible polymer, the monomers other than benzyl acrylate and benzylmethacrylate are preferably acrylic acid and/or methacrylic acid andother acrylates and/or methacrylates. The polymer is preferablycopolymerized from just these monomers.

Examples of acrylates and methacrylates that may be used in theinvention include commercially available (meth)acrylates, such as methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl(meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate,2-ethylhexylcarbitol (meth)acrylate, phenol EO modified (meth)acrylate,N-vinylpyrrolidone, isobornyl (meth)acrylate, benzyl (meth)acrylate,paracumylphenol EO modified (meth)acrylate,2-hydroxyethyl-3-phenoxypropyl (meth)acrylate, etc. Also, in place ofacrylic acid and methacrylic acid, w-carboxy-polycaprolactonemono(meth)acrylate, phthalic acid monohydroxyethyl (meth)acrylate,(meth)acrylic acid dimer, etc. The benzyl-group-containing waterdispersible polymer has a styrene-equivalent number average molecularweight of preferably no less than 20000 and no more than 200000 and morepreferably no less than 20000 and no more than 100000. Butyl(meth)acrylate is preferably contained as the (meth)acrylate.

(Acrylic Acid-Acrylate-Based Water Dispersible Polymer)

The present water dispersible polymer is preferably a copolymer with amonomer composition wherein the proportion of acrylate and acrylic acidwith respect to the total monomer weight is no less than 80%. When thisproportion is less than 80%, the fixing and gloss properties onspecialized paper are lowered. The proportion is more preferably no lessthan 90% and even more preferably 100%. Examples of acrylates that maybe used include commercially available acrylates, such as methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexylacrylate, cyclohexyl acrylate, octyl acrylate, lauryl acrylate,2-ethylhexyl acrylate, 2-ethylhexylcarbitol acrylate, phenol EO modifiedacrylate, N-vinylpyrrolidone, isobornyl acrylate, benzyl acrylate,paracumylphenol EO modified acrylate, 2-hydroxyethyl-3-phenoxypropylacrylate, etc. Also, in place of acrylic acid,ω-carboxy-polycaprolactone monoacrylate, phthalic acid monohydroxyethylacrylate, acrylic acid dimer, etc., may be used. Preferably, benzylacrylate and/or butyl acrylate is used. More preferably, the polymer isa copolymer of monomers containing benzyl acrylate at a proportion of noless than 40% and no more than 80% of the total monomer weight. Theacrylic acid-acrylate-based water dispersible polymer has astyrene-equivalent number average molecular weight of preferably no lessthan 20000 and no more than 200000 and more preferably no less than20000 and no more than 100000.

(Water Dispersible Polymer Having Paracumylphenoxyethylene GlycolAcrylate as a Monomer)

Also, the present water dispersible polymer is preferably a copolymerusing paracumylphenoxyethylene glycol acrylate as a monomer. Bycontaining paracumylphenoxyethylene glycol acrylate, since therefractive index of the polymer is improved and yet the glass transitiontemperature is not increased, the gloss and fixing properties on glossypaper improve. Preferably, the proportion of this monomer with respectto the total monomer weight is no less than 10%, more preferably no lessthan 20%, even more preferably no less than 30%, and yet even morepreferably no less than 50%.

With a water dispersible polymer containing paracumylphenoxyethyleneglycol acrylate as a monomer component, the polymer is preferably acopolymer, wherein the total amount of paracumylphenoxyethylene glycolacrylate, acrylates other than paracumylphenoxyethylene glycol acrylate,and acrylic acid with respect to the total monomer weight is no lessthan 80%. If this amount is no less than 80%, the fixing and glossproperties on specialized paper will be lowered. The amount is morepreferably no less than 90% and even more preferably 100%. Though as theabovementioned other acrylates, one or two or more types among thevarious acrylates mentioned above may be used, benzyl acrylate and/orbutyl acrylate is preferably contained.

The copolymer containing paracumylphenoxyethylene glycol acrylate as amonomer component preferably has a refractive index of no less than1.50. When the refractive index is no less than 1.50, the coloration onregular paper and the gloss and fixing properties on glossy paper areimproved. The refractive index may be measured by preparing a film-likesample, with which solvent and water have been removed from the polymer,and measuring with a refractometer (for example, Abbe's refractometer3T) or a measuring device of equivalent precision. This copolymer waterdispersible polymer has a styrene-equivalent number average molecularweight of preferably no less than 20000 and no more than 200000 and morepreferably no less than 20000 and no more than 100000.

(Sulfur-Containing Water Dispersible Polymer)

The present water dispersible polymer preferably contains sulfur (S) atan amount of no less than 1% and no more than 20% of the total weight ofthe polymer. At an amount less than 1%, though the refractive index canbe improved by other components, the fixing property is lowered, and inthe excess of 20%, dispersion becomes unstable and difficult to achieve.More preferably, the lower limit is no less than 3% and the upper limitis no more than 15%. The sulfur in the polymer can be measured byelemental analysis using the 2400CHN Elemental Analyzer (made by PerkinElmer Inc. (USA)) or a measurement device by which a similar precisioncan be obtained.

This sulfur-containing water dispersible polymer is preferably acopolymer of monomers, mainly comprising a sulfur-containing monomer, anacrylate, and acrylic acid or monomers formed from such monomers. Theacrylate here does not include the sulfur-containing monomer even if thesulfur-containing monomer is an acrylate. That is, this acrylate is anacrylate that does not contain sulfur. As the sulfur-containing monomer,a monomer, having an acryloyl group, methacryloyl group, vinyl group, oraryl group that has a double bond and wherein an oxygen atom has beenreplaced by a sulfur atom, may be used. Specifically, variousthioacrylates and/or thiomethacrylates may be used as thesulfur-containing monomer. Thiomethacrylates are preferably used andamong these, the use of phenyl thiomethacrylate is preferable.

As the acrylate in the sulfur-containing water dispersible polymer, oneor two or more types among the various acrylates mentioned above may beused. Benzyl acrylate and/or butyl acrylate is preferably contained. Thesulfur-containing water dispersible polymer also preferably has arefractive index of no less than 1.50 from the standpoint of colorationon regular paper and gloss and fixing properties on glossy paper. Thissulfur-containing water dispersible polymer has a styrene-equivalentnumber average molecular weight of preferably no less than 20000 and nomore than 200000 and more preferably no less than 10000 and no more than100000.

(Urethane-Based Water Dispersible Polymer)

The present water dispersible polymer is preferably a copolymer ofmonomers, including at least in part, an urethane acrylate and/orurethane methacrylate, a non-urethane acrylate and/or non-urethanemethacrylate, and acrylic acid and/or methacrylic acid as monomercomponents, with the total amount of allophanate bonds and biuret bondswith respect to the polymer solids being no more than 1.0 mmol/g and thetotal amount of urethane bonds, urea bonds, allophanate bonds, andbiuret bonds with respect to the polymer solids being preferably no morethan 10.0 mmol/g.

The urethane-based water-dispersible polymer is a copolymer that iscopolymerized with an urethane acrylate and/or urethane methacrylate anda non-urethane acrylate and/or non-urethane methacrylate as maincomponents and having a carboxylic-group-containing monomer as a monomercomponent. Though the urethane-based water dispersible polymer maycontain other monomer components, it preferably has just the polymerizedunits of the above. With the urethane-based water dispersible polymer,the proportion of the urethane (meth)acrylate and non-urethane(meth)acrylate monomers among the total monomers that are polymerized ispreferably no less than 80%. This is because when this monomerproportion is no less than 80%, adequate dispersion stability and glossand fixing properties on glossy paper can be obtained. Theabove-mentioned proportion is more preferably no less than 85%. Theproportion of these (meth)acrylate monomers is preferably no more than98% and more preferably no more than 95%. This is because otherwise, thedispersibility in water is lowered due to the relationship with thecarboxylic-group-containing monomer. The proportion of (meth)acrylicacid or other carboxylic-group-containing monomer is preferably no lessthan 5% and no more than 10%. This is because, when this proportion isno less than 5% and no more than 10%, adequate dispersibility in waterand adequate coloration can be secured.

Also, with the urethane-based water dispersible polymer, the proportionof a urethane (meth)acrylate monomer is preferably no less than 1.0% andno more than 50%. When this proportion is less then 1.0%, the fixingproperty is poor, and in the excess of 50%, the viscosity becomes toohigh with an aqueous system such as that of this invention anddispersion in water becomes unstable. Furthermore, the present polymerpreferably does not have polymerization units of aromatic vinylmonomers, such as styrene, 2-methylstyrene, vinyltoluene,t-butylstyrene, chlorostyrene, vinylanisole, vinylnaphthalene, etc. Bynot containing styrene monomer units, yellowing of recorded images,etc., can be avoided.

With the urethane-based water dispersible polymer, just acrylates arepreferably used as the urethane (meth)acrylate and the non-urethane(meth)acrylate. This is because by using acrylates, the gloss propertyon glossy paper can be improved. Also, though acrylic acid and/ormethacrylic acid may be used as the carboxylic-group containing monomer,preferably just acrylic acid is used.

The urethane-based water dispersible polymer can be obtained bypolymerizing the following polymerizable monomers (including oligomers).

(Non-urethane (meth)acrylate)

“Non-urethane (meth)acrylate” refers to a (meth)acrylate other thanurethane (meth)acrylates. Though not restricted in particular, forexample, a (meth)acrylate that is a branched or unbranched chainaliphatic ester, alicyclic ester, or aromatic ester, etc., of(meth)acrylic acid may be used, and specific examples that may be usedinclude methyl (meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate, ethylhexyl (meth)acrylate, n-butyl (meth)acrylate,isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate,n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hexyl(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl(meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl(meth)acrylate, octadecyl (meth)acrylate, 2-ethylhexylcarbitol(meth)acrylate, phenol EO modified (meth)acrylate, N-pyrrolidone,paracumyl EO modified (meth) acrylate, 2-hydroxyethyl-3-phenoxypropyl(meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate,isobornyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate,ethoxy-group-containing diethylene glycol (meth)acrylates,propoxy-group-containing diethylene glycol (meth)acrylates,butoxy-group-containing diethylene glycol (meth)acrylates,ethoxy-group-containing polyethylene glycol (meth)acrylates,propoxy-group-containing polyethylene glycol (meth)acrylates,butoxy-group-containing polyethylene glycol (meth)acrylates,hydroxyalkyl methacrylates, hydroxyalkyl acrylates, dimethylaminomethacrylate, dimethylamino acrylate, and dimethylaminoethylmethacrylate.

As an alkyl (meth)acrylate, a straight chain or branched alkyl(meth)acrylate with 2 to 12 carbons may be used, as a cycloalkyl(meth)acrylate, a cycloalkyl (which may be substituted with an alkylgroup with 1 or 2 carbons) (meth)acrylate with 5 to 7 carbons may beused, and as an aromatic (meth)acrylate, a (meth)acrylate, having asingle aromatic ring (which may have an alkenyl group), may be usedfavorably.

One type of these various (meth)acrylates may be used or two or moretypes may be used in combination. Preferably, one type or two or moretypes selected from among the abovementioned alkyl (meth)acrylates,cycloalkyl (meth)acrylates, and aromatic (meth)acrylates is or are used,and more preferably just these acrylates are used. Examples of suchpreferable acrylates include n-butyl acrylate, benzyl acrylate,cyclohexyl acrylate, isobornyl acrylate, lauryl acrylate, and2-ethylhexyl acrylate.

(Urethane (meth)acrylate)

The present polymer may contain a predetermined amount of urethanebonds, urea bonds, allophanate bonds, and biuret bonds, and such bondsare preferably supplied to the present polymer by a urethane(meth)acrylate. The urethane chain part of a urethane (meth)acrylate atleast contains a urethane bond and contains any or two or more types ofbonds among urea bonds, allophanate bonds, and biuret bonds.

A urethane (meth)acrylate may take any of various forms. For example, aurethane (meth)acrylate may be obtained by reacting a urethane oligomer,obtained by the reaction of an organic polyisocyanate and a diol or of adiol and a diamine, with a hydroxyl-group-containing (meth)acrylate. Inthe present polymer, either or both of a urethane acrylate and aurethane methacrylate may be used. It is more preferable to use just aurethane acrylate.

(Urethane Oligomer)

As an organic polyisocyanate for obtaining a urethane oligomer, a knownaliphatic diisocyanate, alicyclic diisocyanate, aromatic isocyanate, ora modified form of any of these may be used. Examples of diisocyanatesinclude trilene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate(MDI), xylylene diisocyanate (XDI), naphthylene diisocyanate (NDI),paraphenylene diisocyanate (PPDI), tetramethylxylylene diisocyanate(TMXDI), hexamethylene diisocyanate cyclohexyl diisocyanate (CHDI),dicyclohexylmethane diisocyanate isophorone diisocyanate lysinediisocyanate (LDI), isopropylidene bis(4-cyclohexyldiisocyanate) (IPC),hydrogenated xylylene diisocyanate (hydrogenated) (XDI), tolidinediisocyanate (TODI), toluoylene diisocyanate, phenylmethanediisocyanate, etc.

Also, in this invention, modified forms of the above, which have or canform a urethane bond, urea bond, allophanate bond, or biuret bond, maybe used. A modified form having a urethane bond is obtained by modifyingan isocyanate monomer or a diisocyanate monomer with a scarce amount ofpolyol, and a modified form having a urea bond is obtained by modifyingan abovementioned monomer with a scarce amount of polyamine. A modifiedform having an allophanate bond is a modified form having an isocyanategroup added to a urethane bond, and a modified form having a biuret bondis a modified form having an isocyanate group added to a urea bond. Suchmodified forms are described for example in Japanese Published ExaminedPatent Application No. S64-10023, Japanese Published Unexamined PatentApplication No. S58-38713, Japanese Published Examined PatentApplication No. S63-89574, Japanese Published Unexamined PatentApplication No. H6-9504, Japanese Published Unexamined PatentApplication No. H4-306218, etc.

As the polyol or polyol and diamine to be reacted with the organicpolyisocyanate, a known polyol compound and/or diamine compound may beused without particular restrictions. Examples of diol compounds includediol compounds, such as ethylene glycol, dipropylene glycol,1,2-butanediol, 1,4-butanediol, 1,6-hexanediol,cyclohexane-1,4-dimethanol, polytetramethylene glycol, and polypropyleneglycol, polyester compounds, which are reaction products of such diolcompounds with a polybasic acid, such as adipic acid, succinicanhydride, isophthalic acid, phthalic anhydride, terephthalic acid,tetrahydrophthalic anhydride, hexahydrophthalic anhydride, azelaic acid,etc., and polycaprolactone diol and other reaction products of theabovementioned diol compounds with ε-caprolactone. Example of diaminecompounds include hexamethylenediamine, 1,7-diaminoheptane,1,8-diaminooctane, 1,9-diaminononane, o-phenylenediamine,m-phenylenediamine, etc. Compounds having a hydroxyl group or an aminogroup as an active hydrogen group may also be used. Also for thesynthesis of a urethane oligomer, isocyanate ethyl (meth)acrylate orother (meth)acrylate, having an isocyanate group as a functional group,may be used.

Examples of hydroxyl-group-containing (meth)acrylates include2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,1,4-butanediol (meth)acrylate, polyethylene glycol (meth)acrylate,polypropylene mono(meth)acrylate, e-caprolactone adduct of2-hydroxyethyl mono(meth)acrylate, 2-hydroxy-3-phenyloxypropyl(meth)acrylate, pentaerythritol (meth)acrylate, etc. With thisinvention, one of the above compounds may be used or two or more of theabove compounds may be used in combination, and preferably ahydroxyl-group-containing acrylate is used.

The amount of urethane bonds, urea bonds, allophanate bonds, and biuretbonds in a urethane (meth)acrylate obtained from a urethane oligomer andan organic polyisocyanate can be adjusted in each of the urethaneoligomer and/or organic polyisocyanate. That is, one skilled in the artcan adjust the contained amount of such bonds by suitable selection ofthe organic polyisocyanate, diol, and, where necessary, diamine andadjustment of the reaction conditions. As already described, the contentof the urethane bonds, etc., in the urethane (meth)acrylate concernedcan be determined by performing back titration, via decompositiontreatment using butylamine, and GC-MS. A urethane (meth)acrylate thatmay be used in this invention may be synthesized as suited or obtainedas a commercially available urethane (meth)acrylate. Examples of suchurethane acrylates and urethane methacrylates include CN961 (made byNippon Kayaku Co., Ltd.), the Beam Set 500 Series (502M, 505A6, 510,550B, 570, etc.), made by Arakawa Chemical Industries, Ltd., SH-500B,made by Negami Chemical Industrial Co., Ltd., etc.

(Carboxylic-Group-Containing Monomer)

The present polymer preferably has a carboxylic group for providinghydrophilicity. As the carboxylic group in the present polymer, acrylicacid, methacrylic acid, crotonic acid, propyl acrylic acid, isopropylacrylic acid, itaconic acid, or fumaric acid may be used.ω-carboxy-polycaprolactone monoacrylate, phthalic acid monohydroxyethylacrylate, acrylic acid dimer, etc., may also be used. Just one of theabove groups may be used or two or more may be used in combination,preferably acrylic acid and/or methacrylic acid is used, and morepreferably acrylic acid is used.

In producing the urethane-based water dispersible polymer, otherpolymerizable monomers may be used within a range in which theachievement of invention's objects will not be obstructed. Examples ofsuch monomers include vinyl ester monomers, such as vinyl acetate, etc.,vinyl cyan compound monomers, such as acrylonitrile, methacrylonitrile,etc., halogenated monomers, such as vinylidene chloride, vinyl chloride,etc., olefin monomers, such as ethylene, propylene, isopropylene, etc.,and diene monomers, such as butadiene, chloroprene, etc. Vinyl monomers,such as vinyl ether, vinyl ketone, vinylpyrrolidone, etc., may also becited as examples.

(Urethane Bonds, Urea Bonds, Allophanate Bonds, and Biuret Bonds)

Though the urethane-based water dispersible polymer has a urethane(meth)acrylate as a polymerization unit and has at least urethane bonds,with the present polymer, the total amount of allophanate bonds andbiuret bonds is preferably no more than 1.0 mmol/g with respect to thepolymer solids. This is because when 1.0 mmol/g is exceeded, thedispersion stability of the pigment degrades significantly. Morepreferably, the abovementioned amount is no more than 0.1 mmol/g. Thatis, from the standpoint of dispersion stability, the monomercomposition, polymerization conditions, etc., are preferably selected sothat allophanate bonds and biuret bonds will not be contained. Also withthe present polymer, the total amount of urethane bonds, urea bonds,allophanate bonds, and biuret bonds with respect to the polymer solidsis preferably no more than 10.0 mmol/g. This is because in the excess of10.0 mmol/g, the dispersion stability of the pigment degrades. The totalamount of these four types of bonds is preferably no less than 0.1mmol/g. This is because at an amount less than 0.1 mmol/g, the fixingproperty on glossy paper is lowered.

Furthermore with the urethane-based water dispersible polymer, the totalamount of urethane groups and urea groups with respect to the polymersolids is preferably no less than 0.8 mmol/g and no more than 1.3mmol/g. This is because within this range, good dispersion stability andgood fixing property on glossy paper can be obtained readily. Even ifthe present polymer contains just urethane bonds, the fixing property onglossy paper and the dispersion stability can be adjusted by controllingthe total amount of these various types of bonds.

(Method for Measuring Urethane Bonds, Urea Bonds, Allophanate Bonds, andBiuret Bonds)

The respective amounts and the respective abovementioned total amountsof the abovementioned bonds in a urethane-based water dispersiblepolymer can be measured as follows. That is, after selectivedecomposition of allophanate and biuret bonds in the present polymer byan amine, the content (equivalents) of these bonds are determined byback titration of the unreacted amine, and by using GC-MS (gaschromatography-mass spectroscopy) on the amine decomposition product,the unreacted urethane bonds and urea bonds, including the urethanebonds and urea bonds generated from the biuret bonds and allophanatebonds by the amine decomposition, are measured. The respective amountsand the various total amounts of the urethane bonds, etc., can thus bedetermined. With the present polymer, n-butylamine may be used todecompose the allophanate bonds and biuret bonds under conditions inwhich the urethane bonds and urea bonds will not be decomposed.Specifically, the quantitative process using n-butylamine may be onewherein an excess amount of n-butylamine is added to the presentpolymer, and after leaving for 24 hours at 40° C., back titration with ahydrochloric acid solution of 0.1% concentration is performed. Thevarious bond amounts and various total amounts may also be measured byanother method as long as accuracy and precision equivalent to those ofthe above-described method can be obtained. Such other methods includemethods of analysis using amine decomposition and then using proton NMRor gas chromatography, methods of performing hydrolysis using a pyridineafter performing amine decomposition, etc. In regard to the measurementof these various bond amounts, etc., reference can be made to KenichiWatanabe et. al., “Quantification of allophanate bonds in thermosettingpolyurethanes by proton nuclear magnetic resonance analysis of aminedecomposition and pyridine decomposition,” Bunseki Kagaku (JapanAnalyst) Vol. 44, No. 1, p. 49 (1995), etc.

(Water-Dispersible Polymer Production Method)

The Above-Described Water-Dispersible Polymers can be Obtained bySolution polymerization or emulsion polymerization. As thepolymerization initiator, potassium persulfate or ammonium persulfatemay be used, and besides these, a general initiator used in radicalpolymerization, such as hydrogen persulfate, azobisisobutyronitrile,azobisisovaleronitrile, azobisacetoxyphenylethane,azobismethylbutanamidodihydrochloride tetrahydrate,azobismethylbutyronitrile, azobiscyclohexanecarbonitrile, dimethylazobisisobutyrate, azobiscyanovaleric acid, benzoyl peroxide, dibutylperoxide, peracetic acid, cumene hydroperoxide, t-butyl hydroxyperoxide,para-menthane hydroxyperoxide, etc., may be used.

Also a chain transfer agent may be added, where necessary in the processof polymerization. Examples of chain transfer agents include mercaptans,such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan,n-hexadecyl mercaptan, n-tetradecyl mercaptan, t-tetradecyl mercaptan,etc.; xanthogen disulfides, such as dimethyl xanthogen disulfide,diethyl xanthogen disulfide, diisopropyl xanthogen disulfide, etc.;thiuram disulfides, such as tetramethyl thiuram disulfide, tetraethylthiuram disulfide, tetrabutyl thiuram disulfide, etc.; halogenatedhydrocarbons, such as carbon tetrachloride, ethylene bromide, etc.;hydrocarbons, such as pentaphenylethane, etc.; unsaturated cyclichydrocarbon compounds, such as acrolein, methacrolein, aryl alcohols,2-ethylhexyl thioglycolate, terpinolene, α-terpinene, γ-terpinene,dipentene, α-methylstyrene dimer (that which has no less than 50 weightparts of 2,4-diphenyl-4-methyl-1-pentene is preferable),9,10-dihydroanthracene, 1,4-dihydronaphthalene, indene,1,4-cyclohexadiene, etc; and unsaturated heterocyclic compounds, such asxanthene, 2,5-dihydrofuran, etc.

In the process of polymerization, a surfactant may be added asnecessary. As the surfactant, sodium lauryl sulfate or potassium laurylsulfate may be used, and besides these, an anionic surfactant, nonionicsurfactant, or amphoteric surfactant may be used.

The polymerization may be carried out as solution polymerization underthe presence of abovementioned polymerization initiator and in asolvent, such as an aliphatic hydrocarbon solvent, aromatic hydrocarbonsolvent, ester solvent, ketone solvent, alcohol solvent, aproticsolvent, etc. The polymerization is normally carried out at 30 to 100°C. and preferably at 50 to 80° C. for 1 to 10 hours, and the conditionsare selected as suited according to the types of polymerizationinitiator, monomer, solvent, etc., that are used. Also, thepolymerization is preferably carried out under nitrogen or other inertgas atmosphere. After polymerization, the copolymer can be isolated by aknown method, such as reprecipitation, solvent distillation, etc. Also,the obtained copolymer can be removed of unreacted monomer, etc., andrefined by reprecipitation, membrane separation, chromatography,extraction, etc.

A polymer with a carboxylic group, such as the present polymer, ispreferably ionized by a neutralizer (alkaline agent). As the neutralizer(alkaline agent), an inorganic alkali, such as sodium hydroxide,potassium hydroxide, lithium hydroxide, etc., or an organic amine, suchas ammonia, trimethylamine, tripropylamine, tributylamine,diethylmethylamine, dipropylmethylamine, dibutylmethylamine,dipropylbutylamine, triethanolamine, tripropanolamine, tributanolamine,etc., may be used.

In synthesizing the present polymer, the composition of thepolymerizable monomers is designed to be a preferable monomercomposition as described above. The present water dispersible polymermay also be prepared while adding one or more types of polymer selectedfrom the group consisting of polyacrylic acid esters, styrene-acrylicacid copolymers, polystyrenes, polyesters, polyamides, polyimides,silicon-containing polymers, and sulfur-containing polymers so that suchpolymers will be components.

The water dispersible polymer of the invention described above ispreferably used as a polymer for dispersing a pigment, used in an inkcomposition for ink jet recording, in water. The water dispersiblepolymer may take any of the abovementioned forms. The preferable form isa copolymer of monomers, mainly comprising a carboxylic-group-containingmonomer and an acrylate and/or methacrylate, having a styrene-equivalentnumber average molecular weight as determined by gel permeationchromatography of no less than 5000 and no more than 200000, and havingany of the following characteristics of (a) to (e) below.

(a) the water dispersible polymer is a copolymer of monomers, havingbenzyl acrylate and/or benzyl methacrylate and having these benzylmonomers at an amount of no less than 40 weight % and no more than 80weight % of the total monomer weight;(b) the water dispersible polymer is a copolymer of monomers, having anacrylate and acrylic acid at an amount of no less than 80 weight % ofthe total monomer weight;(c) the water dispersible polymer is a copolymer of monomers, containingparacumylphenoxyethylene glycol acrylate at least in part;(d) the water dispersible polymer contains sulfur (S) at an amount of noless than 1 weight % and no more than 20 weight % of the total weightthereof,(e) the water dispersible polymer is a polymer of monomers, containing aurethane acrylate and/or a urethane methacrylate, a non-urethaneacrylate and/or a non-urethane methacrylate, and acrylic acid and/ormethacrylic acid at least in part, the total amount of allophanate bondsand biuret bonds with respect to the polymer solids is no more than 1.0mmol/g, and the total amount of urethane bonds, urea bonds, allophanatebonds, and biuret bonds with respect to the polymer solids is no morethan 10.0 mmol/g.

The various water-dispersible polymers of (a) to (e) above may take onthe various forms described above.

(Polymer-Coated Pigment)

In the present aqueous ink composition, the abovementioned pigmentpreferably exists as a polymer-coated pigment (may also be referred toas “microcapsulated pigment”) that is coated with a water-dispersiblepolymer. The polymer-coated pigment is dispersible in an aqueous mediumin the form wherein the pigment is coated or surrounded by the polymercompound. This polymer-coated pigment especially preferably has apigment mentioned below coated by the polymer compound. As the pigment,carbon black is preferable in the case of black ink, one or more typesof pigment selected from the group consisting of C. I. Pigment Blue15:1, C. I. Pigment Blue 15:3, and C. I. Pigment 15:4 is preferable inthe case of cyan ink, one or more types of pigment selected from thegroup consisting of C. I. Pigment Red 122, C. I. Pigment Red 146, C. I.Pigment Red 169, C. I. Pigment Red 81:2, C. I. Pigment Red 176, C. I.Pigment Red 184, C. I. Pigment Red 185, C. I. Pigment Red 202, C. I.Pigment Red 208, C. I. Pigment Red 57:1, C. I. Pigment Violet 32, and C.I. Pigment Violet 19 is preferable in the case of magenta ink, and oneor more types of pigment selected from the group consisting of C. I.Pigment Yellow 73, C. I. Pigment Yellow 74, C. I. Pigment Yellow 109, C.I. Pigment Yellow 110, C. I. Pigment Yellow 128, C. I. Pigment Yellow129, C. I. Pigment Yellow 138, C. I. Pigment Yellow 150, C. I. PigmentYellow 151, C. I. Pigment Yellow 154, C. I. Pigment Yellow 155, C. I.Pigment Yellow 180, C. I. Pigment Yellow 185, etc., is preferable in thecase of yellow ink. The content of the polymer-coated pigment in theaqueous ink composition as concentration of the polymer-coated pigmentis preferably in the range of no less than 2% and no more than 8% andmore preferably in the range of no less than 3% and no more than 8%.

Among the water-dispersible polymers for the polymer-coated pigment,polymers, having a carboxylic-group as a hydrophilic group and whereinthe monomer composition, amount of urethane bonds, etc., are controlled,exhibit excellent dispersion stability, coloration properties on regularpaper, and gloss and fixing properties on glossy paper when enclosing apigment. Though any of the above-described water-dispersible polymers ispreferably used singly as the polymer coating the pigment, besides sucha polymer, one type of polymer or two or more types of polymers selectedfrom the group consisting of poly(meth)acrylic acid esters,styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid estercopolymers, styrene-(meth)acrylic acid ester-(meth)acrylic acidcopolymers, styrene-maleic acid copolymers, styrene-maleic acidester-maleic acid copolymers, styrene-itaconic acid copolymers,styrene-itaconic acid ester-itaconic acid copolymers,styrene-(meth)acrylic acid ester-itaconic acid copolymers,styrene-fumaric acid copolymers, styrene-fumaric acid ester-fumaric acidcopolymers, and other vinyl polymers, polyesters, polyamides,polyimides, polyurethanes, amino-based polymers, silicon-containingpolymers, sulfur-containing polymers, fluorine-containing-polymers,epoxy resins, etc., may be used in combination.

The average particle diameter of the polymer-coated pigment ispreferably no more than 400 nm and more preferably no more than 200 nm.This is because the dispersion stability decreases significantly whenthe particle diameter exceeds 200 nm. The particle diameter is even morepreferably no more than 150 nm and most preferably no more than 100 nm.Also, the particle diameter is preferably no less than 30 nm. This isbecause the dispersion stability decreases significantly when theparticle diameter is less than 30 nm. More preferably, the particlediameter is no less than 50 nm. Though the average particle diameter ofthe polymer-coated pigment can be measured by a light scattering method,the average particle diameter may also be measured employing anothermethod by which measurements can be made with the same accuracy andprecision. In measuring the average particle diameter by a lightscattering method, for example, the Zetasizer 3000HS (made by MalvernInstruments, Inc. (UK)) may be used.

(Polymer-Coated Pigment Production Method)

The polymer-coated pigment is produced by a known physical-mechanicalmethod or chemical method. Specifically, a phase separation method(coacervation), in-liquid drying method (interface precipitationmethod), spray drying method, pan coating method, in-liquid curingcoating method, interface polymerization method, in situ method,ultrasonic method, etc., may be used without restrictions in particular.As the polymer-coated pigment of the present ink composition, an anionicpolymer-coated pigment described in Japanese Published Unexamined PatentApplication No. H9-151342 may be used. The polymer-coated pigment mayalso be obtained by the method described in Japanese PublishedUnexamined Patent Application No. H10-316909.

(Polymer Coating of Pigment by Polymerization)

The polymer-coated pigment may, for example, be obtained by polymerizingthe monomers of this invention's water-dispersible polymer by emulsionpolymerization under the presence of a pigment. That is, apolymerization reaction is carried out under predetermined conditionsupon adding polymerizable monomers, a polymerization initiator, and,where necessary, a chain transfer agent to a system in which the pigmentis dispersed. The pigment dispersion system may be arranged using adispersant having a polymerizable group that can be copolymerized withanother monomer. Specifically, the pigment, water, and where necessary,a polymerizable surfactant are placed in a reaction vessel, equippedwith an ultrasonic generator, a stirrer, and a temperature regulator,and a pulverization process is carried out by irradiating ultrasonicwaves over a predetermined amount of time. Besides using an ultrasonicdispersion method using an ultrasonic generator, a dispersion methodusing a ball mill, roll mill, Eiger mill or other generally-useddispersion machine or a dispersion method using a high-speed mixer,beads mill, sand mill, or roll mill, etc., may be used. Thepolymer-coated pigment can then be obtained favorably by adding monomersand the polymerization initiator and carrying out the polymerizationreaction under a predetermined polymerization temperature. Theabovementioned chain transfer agent may be added to the reaction vesselat this point.

(Polymer Coating of Pigment by a Phase Inversion Emulsification Method)

A phase inversion emulsification method may be cited as a favorablemethod for producing the polymer-coated pigment. By lowering thehydrophilicity of the polymer, the adsorption onto the surface of thepigment, which is high in hydrophobicity, is improved and the pigmentbecomes less likely to be attacked by surfactants and solvents that arenormally used in ink jets and is thereby improved in stability. Whilethe stability of the ink is not obtained with normal dispersion in amedium using an acrylic styrene-based polymer, the stability of the inkis improved and coloration on regular paper is improved by using a phaseinversion emulsification method with this invention's water dispersiblepolymer

The water dispersible polymer that is used in the phase inversionemulsification method is preferably synthesized by solutionpolymerization. It is also preferable for the polymer to be synthesizedby liquid polymerization using a radical polymerization initiator. Thepolymer dispersion obtained by solution polymerization may be used as itis in a pigment dispersion step. As an example of the phase inversionemulsification method, a method comprising: a pigment dispersion step ofpreparing a mixed liquid containing a polymer, a pigment, an organicsolvent, and an excess amount of water with respect to the organicsolvent and dispersing the abovementioned pigment, with at least a partof the abovementioned polymer enclosing the abovementioned pigment, inthe aqueous phase of the abovementioned mixed liquid; and a compositionpreparation step of preparing an aqueous ink composition using thepolymer and the pigment, existing in the abovementioned aqueous phase,along with at least a part of the abovementioned aqueous phase or in astate of separation from the abovementioned aqueous phase; may be cited.

The pigment dispersion process may, for example, be carried out asfollows. That is, a pigment dispersion is prepared by dispersing thepigment in the organic solvent, a polymer dispersion is prepared bydispersing or dissolving the polymer in water, and by mixing the pigmentdispersion and the polymer dispersion, a state, wherein the polymer ismade to exist in a biased manner close to the surface of the pigment andthereby coat the pigment, is formed in the aqueous phase to disperse thepigment. Also, by preparing the organic solvent dispersion containingthe pigment and the polymer (and containing, where suitable, any of aneutralizer, water, and surfactant or a combination of these) and mixingthis with a large amount of water (preferably an excess amount withrespect to the organic solvent), phase inversion emulsification of thepigment and the polymer from the organic solvent phase to the aqueousphase can be achieved to thereby coat (enclose) the pigment with (in)the polymer.

Though the organic solvent that makes up the abovementioned pigmentdispersion is not restricted in particular, an organic solvent of lowboiling point is preferable in view of the ease of distilling off of theorganic solvent. Ketone organic solvents, such as acetone, methyl ethylketone, etc., ester organic solvents, such as ethyl acetate, etc,alcohol organic solvents, such as ethanol, isopropyl alcohol, etc.,aromatic hydrocarbon organic solvent, such as benzene, etc., can becited as examples. Besides the use of ultrasonic waves, a high-speedmixer, sand mill, beads mill, or roll mill, etc., may be selected assuited for use in dispersion of the pigment in the solvent.

Though as mentioned above, among various inorganic alkalis and variousorganic amines, an inorganic alkali is preferably used for thedissolution or dispersion of a polymer with a carboxylic group in water.

The pigment dispersion process in the above-described phase inversionemulsification method is preferably carried out with a device thatperforms mixing and stirring while applying a suitable shear so that thepolymer and the pigment will contact each other and the polymer canbecome attached to the surface of the pigment. Besides removing thesolvent from the mixed liquid of the pigment dispersion and the aqueouspolymer solution by a method such as heating, etc., a method, such ascentrifugation, water washing, ultrafiltration, pressurized filtration,etc., may be selected as suited for separating the polymer and thepigment from the aqueous phase.

This invention thus provides an aqueous ink composition productionmethod comprising: a step of synthesizing a water dispersible polymer(which is preferably a solution polymerization step, more preferablyusing a radical polymerization initiator), a pigment dispersion step ofpreparing a mixed liquid containing the abovementioned polymer, apigment, an organic solvent, and an excess amount of water with respectto the organic solvent and dispersing the abovementioned pigment, withat least a part of the abovementioned polymer being coated on theabovementioned pigment, in the aqueous phase of the abovementioned mixedliquid; and a composition preparation step of preparing an aqueous inkcomposition using the polymer and the pigment, existing in theabovementioned aqueous phase, along with at least a part of theabovementioned aqueous phase or in a state of separation from theabovementioned aqueous phase.

With the present ink composition, besides being dispersed by the presentpolymer, the pigment may also be dispersed by another polymerdispersant. Examples of the polymer dispersant include acrylic-basedresins, such as polyvinyl alcohols, polyvinylpyrrolidones, polyacrylicacids, acrylic acid-acrylonitrile copolymers, potassiumacrylate-acrylonitrile copolymers, vinyl acetate-acrylic acid estercopolymers, acrylic acid-acrylic acid ester copolymers, etc.,styrene-acrylic resins, such as styrene-acrylic acid copolymers,styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylicacid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers,styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers,etc., styrene-maleic acid copolymers, styrene-maleic anhydridecopolymers, vinylnaphthalene-acrylic acid copolymers, vinylnaphthalene-maleic acid copolymers, vinyl-acetate-based copolymers, suchas vinyl acetate-ethylene copolymers, vinyl acetate-fatty acid vinylethylene copolymers, vinyl acetate-maleic acid ester copolymers, vinylacetate-crotonic acid copolymers, vinyl acetate-acrylic acid copolymers,and salts of such resins. Preferably, an acrylic-based resin, such as apolyvinylpyrrolidone, polyacrylic acid, acrylic acid-acrylonitrilecopolymer, potassium acrylate-acrylonitrile copolymer, vinylacetate-acrylic acid ester copolymer, acrylic acid-acrylic acid estercopolymer, etc., is used. The amount added of such a dispersant withrespect to the pigment is preferably in the range of no less than 1% andno more than 50% and more preferably in the range of no less than 2% andno more than 30%.

The dispersion of the pigment by the water dispersible polymer or adispersant containing the water dispersible polymer is carried out bysubjecting a colorant, the abovementioned dispersant, water, and awater-soluble organic solvent to dispersion by a ball mill, sand mill,attritor, roll mill, agitator mill, Henschel mixer, colloid mill,ultrasonic homogenizer, jet mill, Angstrom mill, or other suitabledispersion machine.

Also, with this invention, polymer microparticles may be added toimprove the fixing property. Preferably, an emulsion, containing polymermicroparticles, is contained. In this case, the fixing property isimproved by the minimum film forming temperature (MFT) of the polymermicroparticles being no more than room temperature. Also, even if theglass transition point is no less than room temperature, the apparentfilm forming temperature may be lowered using a film-forming aid.Furthermore, in regard to the method of producing the polymermicroparticles, micro-phase separation structures, wherein hard segmentsand soft segments are separated from each other, can be introduced bypolymerization using a long-chain macromer to improve the fixingproperty.

Such polymer microparticles can be obtained by emulsion polymerizationof a known vinyl monomer. Styrene, tetrahydrofurfuryl acrylate, or butylmethacrylate may be used as the vinyl monomer, and examples of monomersthat can be used besides these include (α, 2, 3, and 4)-alkylstyrenes,(α, 2, 3, and 4)-alkoxystyrenes, 3,4-dimethylstyrenes, α-phenylstyrene,divinylbenzene, vinylnaphthalene, dimethylamino(meth)acrylate,dimethylaminoethyl (meth)acrylate, dimethylaminopropylacrylamide,N,N-dimethylaminoethyl acrylate, acryloyl morpholine,N,N-dimethylacrylamide, N-isopropylacrylamide, N,N-diethylacrylamide,methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,ethylhexyl (meth)acrylate, other alkyl (meth)acrylates, (meth)acrylatesof diethylene glycols or polyethylene glycols with an ethoxy group,propoxy group, or butoxy group, cyclohexyl (meth)acrylate, benzyl(meth)acrylate, phenoxyethyl (meth)acrylate, isobornyl (meth)acrylate,hydroxyalkyl (meth)acrylates, other fluorine-containing,chlorine-containing, and silicon-containing (meth)acrylates,(meth)acrylamide, and maleic acid amide, and in the case where acrosslinked structure is to be introduced in addition to a singlefunctional group of (meth)acrylic acid, (mono, di, tri, tetra, orpoly)ethylene glycol di(meth)acrylate, methacrylates of 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, and 1,10-decanediol,etc., trimethylolpropane tri(meth)acrylate, glycerin (di,tri)(meth)acrylate, di(meth)acrylates of the ethylene oxide adducts ofbisphenol A or F, neopentyl glycol di(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate and othercompounds with an acrylic group or methacrylic group may be used.

Such polymer microparticles can be synthesized by a known emulsionpolymerization method. Sodium lauryl sulfate or potassium lauryl sulfatemay be used as the emulsifier in the synthesis of the polymermicroparticles, and besides these, a surfactant that is a sulfate saltof an alkyl group, branched alkyl group, or alkylphenyl group, having astearyl group, nonyl group, octyl group, etc., or a phosphoric acid saltor boric acid salt surfactant, anionic surfactant, nonionic surfactant,or amphoteric surfactant, etc., may be used.

Potassium persulfate or ammonium persulfate may be used as thepolymerization initiator, and besides these, a general initiator used inradical polymerization, such as hydrogen persulfate,azobisisobutyronitrile, azobisisovaleronitrile, benzoyl peroxide,dibutyl peroxide, peracetic acid, cumene hydroperoxide, t-butylhydroxyperoxide, para-menthane hydroxyperoxide, etc., may be used, andpreferably the initiator is soluble in water since the polymerizationreaction is carried out in water.

Also, t-dodecyl mercaptan may be used as the chain transfer agent, aswell as a generally used chain transfer agent, such as n-dodecylmercaptan or n-octyl mercaptan, a xanthogen, such as dimethyl xanthogendisulfide or diisobutyl xanthogen disulfide, or dipentene, indene,1,4-cyclohexadiene, dihydrofuran, xanthene, etc.

Also, core-shell type polymer microparticles, in which the core andshell differ in structure, may be used. It is preferable to make theminimum film formation temperature (MFT) of such polymer microparticlesno more than room temperature by design or by use of an MFT loweringagent (film-forming aid). Also, depending on the reaction conditions,etc., the abovementioned additives do not have to be used. A suitableselection can be made, for example, in a case where a micelle-formingmonomer is used, a micelle-forming agent is unnecessary, and a chaintransfer agent also may not have to be used depending on the reactionconditions.

This invention's aqueous ink composition contains water and awater-soluble organic solvent. This water and water-soluble organicsolvent form, for example, at least a part of an aqueous medium that isused for the dispersion of a pigment. Polar solvents, such as2-pyrrolidone, N-methylpyrrolidone, ε-caprolactam, dimethyl sulfoxide,sulfolane, morpholine, N-ethyl morpholine, 1,3-dimethyl-2-imidazoline,etc., may be cited as examples of a water-soluble organic solvent, andit is preferable to select and use one or more solvents from suchsolvents. The content of such a polar solvent with respect to the totalweight of the ink for ink jet recording is preferably 0.01 weight % to20 weight % and more preferably 1 weight % to 10 weight %.

The present aqueous ink composition is preferably used as ink for normalwriting utensils as well as for ink jet recording. In use as an inkcomposition for ink jet recording, various types of additives, such as ahumectant, dissolution aid, penetration controlling agent, viscositymodifier, pH adjustor, antioxidant, preservative, antifungal agent,corrosion inhibitor, chelate for capturing metal ions that affectdispersion, etc., may be added for the purpose of securing shelfstability, stable discharge from an ink head, improvement in regard toclogging, or prevention of ink degradation.

In using the present aqueous ink composition as ink jet recording ink,it is preferable for a humectant, comprising a high-boiling-pointwater-soluble organic solvent, to be contained for the purpose ofproviding water retention and wetting properties. A high-boiling-pointwater-soluble organic solvent may be used as a wetting agent, withexamples including polyvalent alcohols, such as ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycol (preferablyof a molecular weight of no more than 2000), propylene glycol,dipropylene glycol, polypropylene glycol, butylene glycol, 1,3-propyleneglycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol,1,3-butaneidiol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol,thioglycol, hexylene glycol, glycerin, meso-erythritol, pentaerythritol,trimethylolpropane, etc. Glycerin and trimethylolpropane may be usedfavorably. One type of such a high-boiling-point water-soluble organicsolvent may be used or two or more types may be mixed and used. Thecontent of such a high-boiling-point water-soluble organic solvent withrespect to the total weight of the ink jet recording ink is preferably0.01 weight % to 20 weight % and more preferably 5 weight % to 20 weight%.

Also in this invention, various types of sugars may be used to restrainthe drying and clogging of ink at the front face of a nozzle.Monosaccharides and polysaccharides may be used, with examples includingglucose, mannose, fructose, ribose, xylose, arabinose, lactose,galactose, aldonic acids, glucitose, maltose, cellobiose, sucrose,trehalose, maltotriose, alginic acid and salts thereof, cyclodextrins,and celluloses. The added amount thereof is preferably no less than0.05% and no more than 30%. At an added amount of less than 0.05%, theeffect of recovery from a clogging phenomenon, wherein the ink dries andclogs the front end of a head, is low, and at an excess of 30%, theviscosity of the ink rises and appropriate printing cannot be performed.The added amount of a general sugar, that is, a monosaccharide orpolysaccharide, such as glucose, mannose, fructose, ribose, xylose,arabinose, lactose, galactose, aldonic acid, glucitose, maltose,cellobiose, sucrose, trehalose, maltotriose, etc., is more preferably 3to 20%. In the case of alginic acid and salts thereof, cyclodextrins,and celluloses, the added amount must be set within a range that theviscosity will not become too high.

The ink composition also preferably contains a penetrating agent for thepurpose of promoting the penetration of the aqueous solvent with respectto a recording medium. By the aqueous solvent penetrating rapidly intothe recording medium, a recorded matter with little blurring of theimage can be obtained without fail. Such a penetrating agent may beselected from among alkyl alcohols with 1 to 4 carbons, such asmethanol, ethanol, etc., alkyl ethers of polyvalent alcohols (alsocalled glycol ethers), such as ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,ethylene glycol monomethyl ether acetate, diethylene glycol monomethylether, diethylene glycol monoethyl ether, ethylene glycol mono-n-propylether, ethylene glycol mono-iso-propyl ether, diethylene glycolmono-iso-propyl ether, ethylene glycol mono-n-butyl ether, diethyleneglycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether,ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butylether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether,propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether,propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propylether, dipropylene glycol monomethyl ether, dipropylene glycol monoethylether, dipropylene glycol mono-n-propyl ether, dipropylene glycolmono-iso-propyl ether, propylene glycol mono-n-butyl ether, dipropyleneglycol mono-n-butyl ether, etc., and straight-chain alkyl diols, such as1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,7-heptanediol, 1,8-octanediol, 1,2-pentanediol, 1,2-hexanediol, etc.An alkylene glycol monoalkyl ether and/or 1,2-alkylene glycol, such asmentioned above may be added to the aqueous ink composition for settingthe surface tension within an appropriate range.

Among the above, an “alkyl ether, with 4 to 10 carbons, of an alkyleneglycol having no more than 10 repeating units,” such as ethylene glycolmono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethyleneglycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether,diethylene glycol mono-t-butyl ether, propylene glycol mono-t-butylether, propylene glycol mono-n-butyl ether, dipropylene glycolmono-n-butyl ether, etc., is preferable, and one or more compoundsselected from the group consisting of diethylene glycol monobutyl ether,triethylene glycol monobutyl ether, dipropylene glycol monobutyl ether,and propylene glycol monobutyl ether is especially preferable.Di(tri)ethylene glycol monobutyl ether is even more preferable. Thecombined use of an 1,2-alkyldiol with 5 to 8 carbons, such as1,2-hexanediol, 1,2-heptanediol, etc., along with or separately of suchan alkyl ether of an alkylene glycol is also preferable. In the casewhere the 1,2-alkyldiol is 1,2-hexanediol and/or 1,2-heptanediol, thedrying of the print is improved by the addition, and since even whencontinuous printing is performed, a previously printed part will notbecome transferred onto the rear surface of a subsequent medium,high-speed printing is enabled, especially in the case of ink jetrecording.

The content of such penetrating agents with respect to the total weightof the ink jet recording ink is preferably no more than 30%, morepreferably no more than 20%, and even more preferably no more than 10%.

In order to set the surface tension within an appropriate range, the inkpreferably contains one or more types of substances selected from thegroup consisting of di(tri)ethylene glycol monobutyl ether,(di)propylene glycol monobutyl ether, and 1,2-alkylene glycols and theadded amount of this substance is preferably no less than 0.5% and nomore than 30%.

Also with this invention's ink, a surfactant may be added to furthercontrol penetration into paper, special paper, or other medium. As thesurfactant to be added, a surfactant of good compatibility with thisinvention's ink system is preferable and that which is high inpermeability and is stable among surfactants is preferable. Amphotericsurfactants, nonionic surfactants, etc., can be cited as examples.Amphoteric surfactants include lauryl dimethylaminoacetic acid betaine,2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaines, palm oilfatty acid amidopropyldimethylaminoacetic acid betaines,polyoctylpolyaminoethyl glycine, and other imidazoline derivatives.Nonionic surfactants include ether-based surfactants, such aspolyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether,polyoxyethylene dodecylphenyl ether, polyoxyethylene alkylaryl ethers,polyoxyethylene oleyl ether, polyoxyethylene lauryl ether,polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers(polyoxypropylene polyoxyethylene alkyl ethers), etc., ester-basedsurfactants, such as polyoxyethylene oleic acid, polyoxyethylene oleicacid esters, polyoxyethylene distearic acid ester, sorbitan laurate,sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate,polyoxyethylene monooleate, polyoxyethylene stearate, as well asfluorine-containing surfactants, such as fluoroalkyl esters,perfluoroalkylcarboxylic acid salts, etc.

The ink composition preferably contains one or more types of surfactantselected from the group consisting of acetylene alcohol surfactants,acetylene glycol surfactants, and silicon-based surfactants. By theaddition of these surfactants, the surface tension can be adjusted to bewithin an appropriate range (no less than 20 mN/m and no more than 40mN/m). By use of these surfactants, blurring on regular paper is reducedin particular and the line width on specialized paper can be adjusted toan appropriate value. The surface tension of an ink composition ispreferably measured by the automatic surface tensiometer Type CBVP-A3(made by Kyowa Interface Science Co., Ltd.) or a measuring device ofequivalent precision.

An acetylene glycol surfactant is preferably used in combination withthe abovementioned glycol ethers. For example, an acetylene glycolcompound, expressed by the following general formula (1) may be used:

In the above formula (1), m and n are numbers that respectively satisfy0=<m+n=<50. R¹, R², R³, and R⁴ respectively and independently indicatealkyl groups (preferably alkyl groups, each with no more than 6carbons). Among the compounds expressed by the above formula (1),2,4,7,9-tetramethyl-5-decene-4,7-diol, 3,6-dimethyl-4-octene-3,6-diol,3,5-dimethyl-1-hexene-3-ol, etc., can be cited as being especiallypreferable. As compounds of the above formula (1), commerciallyavailable products that are sold as acetylene glycol surfactants may beused, with specific examples including Surfynol 104, 82, 440, 465, 485,and STG (all available from Air Products and Chemicals, Inc.) and OlfinSTG and Olfin E1010 (made by Nissin Chemical Industry Co., Ltd.).

Olfin P and Olfin B (made by Air Products and Chemicals, Inc.) andSurfynol 61 (made by Nissin Chemical Industry Co., Ltd.) may be cited asspecific examples of acetylene alcohol surfactants. In using anacetylene alcohol surfactant, a dissolution aid may also be used.Preferable examples of a dissolution aid includedimethyl-2-imidazolidinone, 2-pyrrolidone, and N-methyl-2-pyrrolidone.Silicon-based surfactants may also be used, with preferable specificexamples including BYK-301, 302, 307, 325, 331, 341, 345, 346, 348, and375 (made by BYK Chemie GmbH). The content of these surfactants withrespect to the total weight of the ink jet recording ink is in the rangeof preferably no less than 0.01% an no more than 10% and more preferablyno less than 0.1% and no more than 5%.

The present aqueous ink composition preferably contains one or morecompounds selected from the group consisting of the abovementionedacetylene glycol surfactants, acetylene alcohol surfactants, andsilicon-based surfactants and one or more compounds selected from amonggroup consisting of di(tri)ethylene glycol monobutyl ether,(di)propylene glycol monobutyl ether, and 1,2-alkylne glycols. It ispreferable for the added amount of the abovementioned one or morecompounds selected from the group consisting of acetylene glycolsurfactants, acetylene alcohol surfactants and silicon-based surfactantsto be 0.01% to 0.5% and the added amount of the one or more compoundsselected from the group consisting of di(tri)ethylene glycol monobutylether, (di)propylene glycol monobutyl ether, and 1,2-alkylne glycols tobe no less than 1%.

Also, examples of pH adjustors, dissolution aids, and antioxidantsinclude diethanolamine, triethanolamine, propanolamine, morpholine, andother amines and modified forms thereof, potassium hydroxide, sodiumhydroxide, lithium hydroxide, and other inorganic salts, ammoniumhydroxide and quaternary ammonium hydroxides (tetramethylammonium,etc.), potassium (bi)carbonate, sodium (bi)carbonate, lithium(bi)carbonate and other carbonates as well as phosphates,N-methyl-2-pyrrolidone, urea, thiourea, tetramethylurea, and otherureas, allophanate, methyl allophanate, and other allophanates, biuret,dimethylbiuret, tetramethylbiuret, and other biurets, L-ascorbic acidand salts thereof, etc. Commercially available antioxidants, ultravioletabsorbers, etc., may also be used. Examples include Ciba Geigy's Tinuvin328, 900, 1130, 384, 292, 123, 144, 622, 770, and 292, Irgacor 252 and153, Irganox 1010, 1076, and 1035, MD 1024, etc., as well as oxides oflanthanides.

Also, examples of viscosity modifiers include rosins, alginic acids,polyvinyl alcohols, hydroxypropylcellulose, carboxymethylcellulose,hydroxyethylcellulose, methylcellulose, polyacrylic acid salts,polyvinylpyrrolidone, arabic gum starch, etc.

Examples of preservatives include alkylisothiazolones,chloroalkylisothiazolones, benzisothiazolone, bromonitroalcohols,oxazolidine compounds and/or chloroxylenol, etc., examples of chelatingagents include ethylenediamine acetic acid salts, nitrilotriacetic acidsalts, etc., and examples of corrosion inhibitors includedicyclohexylammonium nitrate, benzotriazole, etc.

As preservatives, products containing octylisothiazolone, which is analkylisothiazolone, as an effective component are commercially available(for example, NS-800H, NS800G, and NS-800P, all made by Nagase ChemteXCorp.). In regard to chloroalkylisothiazolones, products containingchloromethylisothiazolone as an effective component are commerciallyavailable (for example, NS-500W, NS-80D, NS-CG, NS-TM, and NS-RS, allmade by Nagase ChemteX Corp.). Products containing benzisothiazolone asan effective component are also commercially available (for example,Proxel BDN, Proxel BD20, Proxel GXL, Proxel LV, and Proxel TN, all madeby Zeneca Inc. (UK), and Denicide BIT and Denicide NIPA, made by NagaseChemteX Corp.). Products containing a bromonitroalcohol as an effectivecomponent are also commercially available (for example, Bronopol,Miacide BT, and Miacide AS, all made by Nagase ChemteX Corp.). Productscontaining chloroxylenol as an effective component are also commerciallyavailable (for example, PCMX, made by Nagase ChemteX Corp.).

Also, as products having oxazolidine compounds or mixtures or modifiedforms of such components as effective components are commerciallyavailable according to application (for example, NS-BP, DenicideBIT-20N, Denicide SPB, Saniset HP, Microstat 5520, Saniset SK2, DenicideNS-100, Denicide BF-1, Denicide C3H, Saniset 161, Denicide CSA, DenicideCST, Denicide C3, Denicide OMP, Denicide XR-6, Denicide NM, MoldenizeN760, Denisat P4, Denisat P-8, and Denisat CHR, all made by NagaseChemteX Corp.). Among these, products having oxazolidine compounds aseffective components, products having chloroisomethylthiazolone as aneffective component, and products having benzisothiazolone as aneffective component are high in effects in aqueous ink. Thesepreservatives are preferably used not in the form of a solitarycomponent but in the form of composite components, wherein two or morecompounds that are not very similar in structure are used, sinceresistive bacteria can then be restrained.

As chelating agents, ethylenediamine acetic acid salts, such as the freeacids, disodium salts, trisodium salts, and tetrasodium salts ofethylenediamine diatetic acid and ethylenediamine tetraacetic acid arecited. Among these disodium salts, trisodium salts, and tetrasodiumsalts are preferable. Also, though nitrilotriacetic acid salts includethe free acid, monosodium salt, disodium salt, and trisodium salt ofnitrilotriacetic acid, the monosodium salt, disodium salt, and trisodiumsalt are preferable. Lithium salts, potassium salts, ammonium salts, andtriethanolamine salts are also effective for aqueous ink. Suchethylenediamine acetic acid salts, nitrilotriacetic acid salts, etc.,provide the effect of preventing metal ions that exist in an ink passageof an ink cartridge or head from causing coagulation and alteration ofdispersions of molecular colorants and polymer microparticles.

The present invention also provides a recording method of depositing thepresent ink composition onto a recording medium and thereby printingonto the recording. With the present recording method, recorded mattersof excellent printing quality are provided. In particular, either orboth of low blurring and high coloration properties on regular paper andadequate coloration and fixing properties on specialized paper areprovided. Furthermore, the recorded matters that are obtained areprovided with robustness of image, which is a characteristic of recordedmatters using pigment ink. Though various printing methods, such as inkjet recording, recording method by a pen or other writing utensil, etc.,may be cited as recording methods, the recording method using thepresent ink composition is preferably an ink jet recording method inparticular, more preferably an ink jet recording method, wherein ink isdischarged by vibration of an electrostrictive element based onelectrical signals, and even more preferably an ink jet recording methodusing a piezo element. Also, since a recorded matter printed by an inkjet recording method using the present ink composition is provided withboth excellent printing quality and image robustness, it is excellent inlong-term stability and favorable as a recorded matter of a photographor other image.

Example 1

Specific examples of this invention shall now be described. The presentinvention is not limited to just these specific examples.

(Production of Dispersions A1 to A4)

First, dispersion A1 uses Monarch 880 (made by Cabot Corp.), which is acarbon black. After performing nitrogen replacement of the interior of areaction vessel, equipped with a stirrer, thermometer, reflux tube, anddripping funnel, 20 parts of styrene, 5 parts of 2-ethylhexylmethacrylate, 15 parts of butyl methacrylate, 10 parts of laurylmethacrylate, 2 parts of methacrylic acid, and 0.3 parts of t-dodecylmercaptan were placed in the reaction vessel and heated to 70° C. Then150 parts of styrene, 15 parts of acrylic acid, 50 parts of butylmethacrylate, 1 part of t-dodecyl mercaptan, 20 parts of methyl ethylketone, and 1 part of azobisisobutyronitrile, which were preparedseparately, were placed in the dripping funnel and dripped into thereaction vessel over a period of 4 hours to carry out a polymerizationreaction of a dispersion polymer. Methyl ethyl ketone was then added tothe reaction vessel to prepare a dispersion polymer solution of aconcentration of 40%.

Upon taking a part of the abovementioned dispersion polymer andsubjecting it to gel permeation chromatography (GPC) using the L7100System made by Hitachi, Ltd., the styrene-equivalent molecular weight asmeasured using THF as the solvent was found to be 50000. The dispersion(Mw/Mn) of the molecular weight was 3.2.

40 parts of the abovementioned dispersion polymer solution, 30 parts ofMonarch 880 (made by Cabot Corp.), which is a carbon black, 100 parts of0.1 mol/L sodium hydroxide aqueous solution, and 30 parts of methylethyl ketone were then mixed and stirred for 30 minutes in ahomogenizer. Thereafter, 300 parts of ion-exchanged water were added andstirring was performed for another hour. The entire amount of methylethyl ketone and a part of the water were then distilled off using arotary evaporator, the pH was adjusted to 9 by neutralization by a 0.1mol/L sodium hydroxide aqueous solution, and filtration through a 0.3 μmmembrane filter was carried out, thereby preparing dispersion A1, havinga solids content (dispersion polymer and carbon black) of 20%.

Dispersions A2 to A4 were obtained by the same method as the above. Eachdispersion was prepared so that the weight ratio of the dispersionpolymer to the pigment will be 20:80. For dispersion A2, Pigment Blue15:3 (copper phthalocyanine pigment made by Clariant, Ltd.) was used.For dispersion A3, Pigment Red 122 (dimethylquinacridone pigment; madeby Clariant, Ltd.) was used. For dispersion A4, Pigment Yellow 180(diketopyrrolopyrrole; made by Clariant, Ltd.) was used.

(Production of Dispersions A5 to A8)

Dispersions A5 to A8 were prepared in the same manner as dispersions A1to A4. For dispersion A5, Leben C (made by Columbian Carbon Ltd.), whichis a carbon black, was used, and for dispersion A6, Pigment Blue 15:4(copper phthalocyanine pigment; made by Clariant, Ltd.) was used. Fordispersion A7, Pigment Violet 19 (quinacridone pigment; made byClariant, Ltd.) was used. For dispersion A8, Pigment Yellow 74(condensed azo pigment; made by Clariant, Ltd.) was used.

(Production of Polymer Particles)

100 parts of ion-exchanged water were placed in a reaction vessel,equipped with a dripping device, thermometer, water-cooled refluxcondenser, and a stirrer, and while stirring at 70° C. under a nitrogenatmosphere, 0.2 parts of potassium persulfate were added as apolymerization initiator. A monomer solution, with which 0.05 parts ofsodium lauryl sulfate, 4 parts of glycidoxy acrylate, 25 parts of benzylmethacrylate, 6 parts of tetrahydrofurfuryl acrylate, 5 parts of butylmethacrylate, and 0.02 parts of t-dodecyl mercaptan were placed in 7parts of ion-exchanged water, was then dripped in and reacted at 70° C.to prepare a primary substance. 2 parts of a 10% ammonium persulfatesolution were then added to the primary substance, stirring wasperformed, and then after adding a reaction solution, comprising 30parts of ion-exchanged water, 0.2 parts of potassium lauryl sulfate, 30parts of styrene, 25 parts of butyl methacrylate, 6 parts of butylacrylate, 2 parts of acrylic acid, 1 part of 1,6-hexanedioldimethacrylate, and 0.5 parts of t-dodecyl mercaptan, while stirring andthereby carrying out a polymerization reaction, the pH was adjusted to 8to 8.5 by neutralization by sodium hydroxide and filtration through a0.3 μm filter was carried out to prepare a 30% aqueous solution ofpolymer microparticles as emulsion A.

(Preparation of Ink Jet Inks)

Examples of compositions that are favorable as ink jet recording ink areindicated below as specific examples of aqueous ink. The added amount ofdispersion is indicated with the amount thereof (solids concentration:total amount of pigment and dispersion polymer) converted to weight. Theparticle diameter of a pigment is indicated in units of nm in < >. 0.05%Topside 240 (made by Permachem Asia Ltd.) in ion-exchanged water forprevention of corrosion of ink, 0.02% benzotriazole in ion-exchangedwater for prevention of corrosion of ink jet head parts, and 0.04% EDTA(ethylenediamine tetraacetic acid) 2Na salt in ion-exchanged water forreducing the effects of metal ions in the ink system were used in theresidual quantity of water in each of the Examples.

The respective ink compositions are shown in Table 1.

TABLE 1 Ink compositions Production Examples A1 A2 A3 A4 A5 A6 A7 A8Dispersion A1 7.5 — — — — — — — Dispersion A2 — 5.0 — — — — — —Dispersion A3 — — 6.5 — — — — — Dispersion A4 — — — 7.0 — — — —Dispersion A5 — — — — 6.0 — — — Dispersion A6 — — — — — 5.0 — —Dispersion A7 — — — — — — 7.0 — Dispersion A8 — — — — — — — 8.0 EmulsionA — — — — 10.0  10.0  10.0  10.0  DEGmBE — 10.0  — — 10.0  — 8.0 10.0 TEGmBE 5.0 — — 3.0 — 6.0 — PGmBE — — — — — — — 2.0 DPGmBE — — — 2.0 — —— 1,2-hexanediol — — 4.0 — — — — — 1,2-pentanediol — — — 5.0 — — — —Glycerin 17.0  17.0  16.0  15.0  14.0  15.0  15.0  9.0  Triethyleneglycol — — 7.0 — 2.0 — — 5.0 Tetraethylene glycol — — 1.5 9.0 — — — —Dipropylene glycol — 5.0 — — — — — — Trimethylolpropane — — — 2.0 — 1.02.0 2-pyrrolidone 5.0 — 2.0 2.0 — 2.0 — — Olfin E1010 1.0 1.2 — — — 1.01.0 — Olfin STG — — 0.5 — — — — 1.0 Surfynol 61 — — — 0.5 — — 0.5 —Triethanolamine 0.8 0.9 1.0 0.7 0.9 0.9 — 0.9 Ion-exchanged waterResidual Residual Residual Residual Residual Residual Residual Residualquantity quantity quantity quantity quantity quantity quantity quantity

In Table 1, the abbreviations indicate the following.

TEGmBE triethylene glycol monobutyl ether

Olfin E10110 (acetylene glycol surfactant, made by Nissin ChemicalIndustry Co., Ltd.)

DEGmBE diethylene glycol monobutyl ether

Olfin STG (acetylene glycol surfactant, made by Nissin Chemical IndustryCo., Ltd.)

Surfynol 61 (acetylene alcohol surfactant, made by Air Products andChemicals, Inc. (USA))

DPGmBE dipropylene glycol monobutyl ether

PGmBE propylene glycol monobutyl ether

(Evaluation of Dispersion Stability)

Table 2 Shows the Percentage Change in Viscosity Upon Leaving for 30Days at 60° C. for each of the aqueous inks prepared by theabove-described methods. Results are shown for the inks of ProductionExamples A1 to A8, and for variations of Production Example A1, in whichthe polymer synthesis method (synthesis time and amount of radicalpolymerization initiator) was varied to vary the respective values ofmolecular weight and the dispersion Mw/Mn, as well as for variations ofProduction Example A1, in which the particle diameter of the pigment wasvaried. The particle diameter was measured using the Zetasizer 3000HS(made by Malvern Instruments, Inc. (UK)). For the percentage change inviscosity, viscosity values were measured at an angle of 60° using theAMVn, made by Anton Paar GmbH, and 1−(value after 30 days)/(initialvalue) is indicated in the form of percentage (%). The OD values weremeasured using the Gretag Macbeth Spectroscan (made by Gretag Corp.).

TABLE 2 Measurement results of percentage change in viscosity ParticlePercentage Production Molecular diameter change in Example weight × 10⁴Mw/Mn (nm) viscosity (%) A1  0.51  3.5  65  1.5  1.12  3.5  60  1.3 3.10  3.5  65  1.0  5.23  3.5  60  1.0 10.21  1.5  60  1.3 10.21  2.0 60  1.0 10.21  3.0  60  1.0 10.21  3.0  15 10.8 10.21  3.0  20  1.010.21  5.0 300  1.9 10.21 10.0  60  1.0 10.21 11.0  60  1.3 20.13  3.5 60  2.6 25.20  3.5  60  3.8 30.11  3.5  60  8.6 A2  5.12  3.0  65  1.0A3  5.56  3.0  70  1.0 A4  5.32  3.5  65  1.0 A5  7.15  3.5  65  1.0 A6 5.28  3.0  65  1.0 A7  5.23  3.0  65  1.0 A8  5.12  3.5  65  1.0

The results of Table 2 show that the storage stability is excellent whenthe colorant is a pigment with a particle diameter as determined by thelight scattering method of no less than 20 nm and no more than 80 nm,and the polymer thereof has a styrene-equivalent molecular weight asdetermined by gel permeation chromatography (GPC) of no less than 20000and no more than 200000 and a dispersion Mw/Mn of 2 to 10, preferably 2to 5, and more preferably 2.5 to 4, as in the present invention. Inregard to the relationships concerning the variations of the respectivevalues of the molecular weight, the dispersion Mw/Mn, and the particlediameter of the pigment, the same trends apply to the ProductionExamples A2 to A8.

(Evaluation of OD on Regular Papers)

Table 3 shows the evaluation results of printing quality on regularpapers. In Production Example A1, the polymerization conditions(synthesis time and amount of radical polymerization initiator) of thepolymer were adjusted to prepare dispersions with different molecularweights, and these dispersions are compared in the Table. The papersused in these evaluations are the commercially available papers, Xerox4024 paper (made by Xerox USA Corp.), Xerox 10 paper (made by Fuji XeroxCo., Ltd.), Ricopy 6200 paper (made by Ricoh Co., Ltd.), and Epson EPPpaper (made by Seiko Epson Co., Ltd.). The OD values were measured bythe same method as that of Table 2.

TABLE 3 OD on regular papers according to polymer molecular weight andpigment concentration Polymer molecular weight × 10⁴ 0.51 3.10 5.2310.21 20.13 30.11 Xerox4024 1.41 1.40 1.40 1.43 1.35 1.21 Xerox10 1.401.40 1.38 1.40 1.34 1.18 Ricopy6200 1.34 1.35 1.35 1.38 1.30 1.16 EPP1.43 1.43 1.43 1.44 1.41 1.22

As is clear from the results of Table 3, a high OD is realized by thepolymer having a styrene-equivalent molecular weight as determined bygel permeation chromatography (GPC) of no more than 200000 as in thepresent invention. In regard to the relationships of dispersions usingpolymers of different molecular weights, the same trends apply toProduction Examples A2 to A8.

(Evaluation of Pigment Concentration and OD)

Table 4 shows the OD values when the pigment concentration is variedwith the inks of Production Examples A1 to 4. The papers used in theseevaluations are the commercially available papers, Xerox 4024 paper(made by Xerox USA Corp.) and Xerox 10 paper (made by Fuji Xerox Co.,Ltd.). The OD values were measured by the same method as that of Table2.

TABLE 4 OD upon variation of pigment concentration Pigment concentration(%) Xerox4024 Xerox10 Production 8.0 1.42 1.42 Example 7.5 1.40 1.40 A14.0 1.22 1.21 3.5 1.09 1.10 Production 5.5 1.35 1.34 Example 5.0 1.331.33 A2 4.0 1.20 1.21 3.5 1.10 1.09 Production 7.0 1.35 1.36 Example 6.51.32 1.32 A3 4.0 1.21 1.20 3.5 1.10 1.10 Production 8.0 1.40 1.41Example 7.0 1.38 1.39 A4 4.0 1.22 1.21 3.5 1.11 1.10

As is clear from the results of Table 4, favorable OD values areobtained when the pigment concentration is no less than 4%.

(Evaluation of Fixing Property and OD on Specialized Paper)

In Production Example A1, the polymerization conditions (synthesis timeand amount of radical polymerization initiator) of the polymer wereadjusted to prepare dispersions with polymers of different molecularweights. The results of evaluation of these dispersions in the fixingproperties and OD values on specialized paper are shown in Table 5. TheOD values were measured by the same method as that of Table 2. Thefixing property was evaluated using specialized paper (PM photo paper)and observing the rubbing off of ink when a printed surface and a rearsurface are overlapped with a load of 300 g and moved at a speed of1m/s. In Table 5, A indicates that there was no rub-off whatsoever, Bindicates that there was slight rub-off C indicates that there wasrub-off and transfer onto the rear surface, and D indicates that therewas considerable rub-off and transfer onto the rear surface.

TABLE 5 Fixing property and OD on specialized paper Molecular weight ×10⁴ 0.51 3.10 5.23 10.21 20.13 30.11 OD 1.8 2.0 2.4 2.5 2.4 1.8Resistance to rubbing C B A A A C

As is clear from the results of Table 5, the fixing property onspecialized paper is improved and a high OD is realized by the polymerhaving a styrene-equivalent molecular weight as determined by gelpermeation chromatography (GPC) of no less than 20000 and no more than200000, as in the present invention. In regard to the relationships ofdispersions using polymers of different molecular weights, the sametrends apply to Production Examples A2 to A8. The Production Examples A5to A8, with which polymer microparticles are added, are better in fixingproperty than Production Examples A1 to A4.

(Evaluation of Discharge Stability)

Table 6 shows the discharge stability evaluation results for the inks ofProduction Examples A1 to A8 and for variations of Production ExampleA1, wherein the composition was varied to vary the surface tension. Thesurface tension was increased by decreasing the added amounts of OlfinE1010, Olfin STG, Surfynol 61, DEGmBE, TEGmBE, PGmBE, and DPGmBE ofTable 1. The surface tension was lowered by the use of thefluorine-based surfactant Futagent 251 (made by Neos Corp.). Surfacetension measurements were made with the automatic surface tensiometerType CBVP-A3 (made by Kyowa Interface Science Co., Ltd.). For evaluationof the discharge stability, the ink jet printer EM-930C, made by SeikoEpson Co., Ltd., was used to perform continuous printing on 100 pages ofA4-size Xerox P paper at 2000 letters/page of Microsoft Word MS Mingstyle characters of style standard size 10. A indicates that no printdistortions occurred, B indicates that print distortions occurred atless than 10 locations, C indicates that print distortions occurred atno less than 10 locations but less than 100, and D indicates that printdistortions occurred at no less than 100 locations.

TABLE 6 Evaluation results of discharge stability Production SurfaceMolecular Example tension weight × 10⁴ Discharge stability A1 19 5.23 D20 5.23 B 30 0.51 B 30 5.23 A 30 30.11 B 41 5.23 C A2 30 5.12 A A3 315.56 A A4 32 5.32 A A5 30 7.15 A A6 29 5.28 A A7 30 5.23 A A8 31 5.12 A

As can be understood from the results of Table 6, the dischargestability is improved by the polymer having a styrene-equivalentmolecular weight as determined by gel permeation chromatography (GPC) ofno less than 20000 and no more than 200000 and a surface tension of noless than 20mN/m and no more than 40mN/m as in the present invention.With regard to the relationships concerning the variation of surfacetension by change of composition, the same trends apply to ProductionExamples A2 to A8.

(Evaluation of Restraining of Material Attack)

In Production Example A1, the polymerization conditions (synthesis timeand amount of radical polymerization initiator) of the polymer wereadjusted to prepare dispersions with polymers of different molecularweights. The results of evaluation of these dispersions in the materialattacking properties are shown in Table 7. Butyl rubber, which is acomponent material of an ink cartridge, was used as the material forevaluation, and the values are shown as weight loss percentage (%) uponleaving for 7 days at 70° C.

TABLE 7 Evaluation results for material attacking property Molecularweight × 10⁴ 0.51 3.10 5.23 10.21 20.13 30.11 Weight loss percentage15.0 3.0 0.1 0.1 0.1 0.1 (%)

As is clear from the results of Table 7, the material attacking propertyis lowered by the polymer having a styrene-equivalent molecular weightas determined by gel permeation chromatography (GPC) of no less than20000 as in the present invention. With regard to the relationshipsconcerning dispersions using polymers of different molecular weights,the same trends apply to Production Examples A2 to A8.

It is thus clear that an aqueous ink, which is excellent in stability,is low in blurring and high in coloration on regular paper, exhibitsadequate coloration as well as fixing property on specialized paper, andis excellent in the discharge stability of ink from an ink jet head andlow in material attacking property in ink jet recording, can be preparedby means of controlling the styrene-equivalent molecular weight of thepolymer as determined by gel permeation chromatography (GPC), theparticle diameter of the pigment, etc., and also controlling themolecular weight dispersion and the surface tension,

Example 2 Production of Dispersions B1 to B4

First, dispersion B1 uses Monarch 880 (made by Cabot Corp.), which is acarbon black. After performing nitrogen replacement of the interior of areaction vessel, equipped with a stirrer, thermometer, reflux tube, anddripping funnel, 20 parts of benzyl methacrylate, 5 parts of2-ethylhexyl methacrylate, 15 parts of butyl methacrylate, 10 parts oflauryl methacrylate, 2 parts of methacrylic acid, and 0.3 parts oft-dodecyl mercaptan were placed in the reaction vessel and heated to 70°C. Then 150 parts of benzyl methacrylate, 15 parts of acrylic acid, 50parts of butyl methacrylate, 1 part of t-dodecyl mercaptan, 20 parts ofmethyl ethyl ketone, and 1 part of azobisisobutyronitrile, which wereprepared separately, were placed in the dripping funnel and dripped intothe reaction vessel over a period of 4 hours to carry out apolymerization reaction of a dispersion polymer. Methyl ethyl ketone wasthen added to the reaction vessel to prepare a dispersion polymersolution of a concentration of 40%.

Upon taking a part of the abovementioned dispersion polymer andsubjecting it to gel permeation chromatography (GPC) using the L7100System made by Hitachi, Ltd., the styrene-equivalent molecular weight asmeasured using THF as the solvent was found to be 50000. The dispersion(Mw/Mn) of the molecular weight was 3.1.

40 parts of the abovementioned dispersion polymer solution, 30 parts ofMonarch 880 (made by Cabot Corp.), which is a carbon black, 100 parts of0.1 mol/L sodium hydroxide aqueous solution, and 30 parts of methylethyl ketone were then mixed and stirred for 30 minutes in ahomogenizer. Thereafter, 300 parts of ion-exchanged water were added andstirring was performed for another hour. The entire amount of methylethyl ketone and a part of the water were then distilled off using arotary evaporator, the pH was adjusted to 9 by neutralization by a 0.1mol/L sodium hydroxide aqueous solution, and filtration through a 0.3 μmmembrane filter was carried out, thereby preparing dispersion B1, havinga solids content (dispersion polymer and carbon black) of 20%.

Dispersions B2 to B4 were prepared in the same manner as describedabove. The weight ratio of the dispersion polymer to the pigment wasadjusted to 20:80. For dispersion B2, Pigment Blue 15:3 (copperphthalocyanine pigment; made by Clariant, Ltd.) was used. For dispersionB3, Pigment Red 122 (dimethylquinacridone pigment; made by Clariant,Ltd.) was used. For dispersion B4, Pigment Yellow 180(diketopyrrolopyrrole; made by Clariant, Ltd.) was used.

(Production of Dispersions B5 to B8)

Dispersions B5 to B8 were prepared in the same manner as dispersions B1to B4, except using a mixture of 50% benzyl methacrylate and 50% benzylacrylate in place of benzyl methacrylate. For dispersion B5, Leben C(made by Columbian Carbon Ltd.), which is a carbon black, was used, andfor dispersion B6, Pigment Blue 15:4 (copper phthalocyanine pigment;made by Clariant, Ltd.) was used for dispersion B7, Pigment Violet 19(quinacridone pigment; made by Clariant, Ltd.) was used. For dispersionB8, Pigment Yellow 74 (condensed azo pigment; made by Clariant, Ltd.)was used.

(Preparation of Ink Jet Inks)

Examples of compositions that are favorable as ink jet recording ink areindicated below as specific examples of aqueous ink. The added amount ofdispersion is indicated with the amount thereof (solids concentration:total amount of pigment and dispersion polymer) converted to weight. Theparticle diameter of a pigment is indicated in units of nm in < >. 0.05%Topside 240 (made by Permachem Asia Ltd.) in ion-exchanged water forprevention of corrosion of ink, 0.02% benzotriazole in ion-exchangedwater for prevention of corrosion of ink jet head parts, and 0.04% EDTA(ethylenediamine tetraacetic acid) 2Na salt in ion-exchanged water forreducing the effects of metal ions in the ink system were used in theresidual quantity of water in each of the Examples. The respective inkcompositions are shown in Table 8.

TABLE 8 Ink compositions Production Examples B1 B2 B3 B4 B5 B6 B7 B8Dispersion B1 7.5 — — — — — — — Dispersion B2 — 4.0 — — — — — —Dispersion B3 — — 6.5 — — — — — Dispersion B4 — — — 6.0 — — — —Dispersion B5 — — — — 8.0 — — — Dispersion B6 — — — — — 5.0 — —Dispersion B7 — — — — — — 6.0 — Dispersion B8 — — — — — — — 8.0 DEGmBE —10.0  — — 10.0  — 8.0 10.0  TEGmBE 5.0 — — 3.0 — 6.0 — PgmBE — — — — — —— 2.0 DPGmBE — — — 2.0 — — — 1,2-hexanediol — — 4.0 — — — — —1,2-pentanediol — — — 5.0 — — — — Glycerin 17.0  17.0  16.0  15.0  14.0 15.0  15.0  9.0 Triethylene glycol — — 7.0 — 2.0 — — 5.0 Tetraethyleneglycol — — 1.5 9.0 — — — — Dipropylene glycol — 5.0 — — — — — —Trimethylolpropane — — — 2.0 — 1.0 2.0 2-pyrrolidone 5.0 — 2.0 2.0 — 2.0— — Olfin E1010 1.0 1.2 — — — 1.0 1.0 — Olfin STG — — 0.5 — — — — 1.0Surfynol 61 — — — 0.5 — — 0.5 — Triethanolamine 0.8 0.9 1.0 0.7 0.9 0.9— 0.9 Ion-exchanged water Residual Residual Residual Residual ResidualResidual Residual Residual quantity quantity quantity quantity quantityquantity quantity quantity In Table 8, the abbreviations indicate thefollowing. TEGmBE: triethylene glycol monobutyl ether Olfin E10110(acetylene glycol surfactant, made by Nissin Chemical Industry Co.,Ltd.) DEGmBE: diethylene glycol monobutyl ether Olfin STG (acetyleneglycol surfactant, made by Nissin Chemical Industry Co., Ltd.) Surfynol61 (acetylene alcohol surfactant, made by Air Products and Chemicals,Inc. (USA)) DPGmBE: dipropylene glycol monobutyl ether PGmBE: propyleneglycol monobutyl ether

(Evaluation of Dispersion Stability)

Table 9 shows the percentage change in viscosity upon leaving for 30days at 60° C. for each of the aqueous inks prepared by theabove-described methods. Results are shown for the inks of ProductionExamples B1 to B8, and for variations of Production Example B1, in whichthe polymer synthesis method (synthesis time and amount of radicalpolymerization initiator) was varied to vary the respective values ofmolecular weight and the dispersion Mw/Mn, as well as for variations ofProduction Example B1, in which the particle diameter of the pigment wasvaried. The particle diameter was measured using the Zetasizer 3000HS(made by Malvern Instruments, Inc. (UK)) (light scattering method). Forthe percentage change in viscosity, viscosity values were measured at anangle of 60° using the AMVn, made by Anton Paar GmbH, and 1−(value after30 days)/(initial value) is indicated in the form of percentage (%). TheOD values were measured using the Gretag Macbeth Spectroscan (made byGretag Corp.).

TABLE 9 Measurement results of percentage change in viscosity PercentageProduction Molecular Particle change in Example weight × 10⁴ Mw/Mndiameter (nm) viscosity (%) B1 0.51 3.1 100 1.4 1.12 3.1 100 1.2 3.103.1 100 1.0 5.23 3.1 100 1.0 10.21 1.3 100 1.2 10.21 2.2 100 1.0 10.213.1 100 1.0 10.21 3.1 15 13.2 10.21 3.2 20 1.0 10.21 5.3 300 1.8 10.2110.5 100 1.0 10.21 11.3 100 1.2 20.13 3.1 100 2.4 25.20 3.1 100 3.530.11 3.1 100 8.1 B2 5.62 3.0 90 1.0 B3 5.96 3.0 95 1.0 B4 5.82 3.5 1001.0 B5 7.35 3.5 100 1.0 B6 7.58 3.0 90 1.0 B7 4.24 3.0 95 1.0 B8 6.133.5 100 1.0

The results of Table 9 show that the storage stability is excellent whenthe colorant is a pigment with a particle diameter as determined by thelight scattering method of no less than 20 nm and no more than 200 nm,and the polymer thereof has a styrene-equivalent molecular weight asdetermined by gel permeation chromatography (GPC) of no less than 20000and no more than 200000 and a dispersion Mw/Mn of 2 to 10, preferably 2to 5, and more preferably 2.5 to 4, as in the present invention. Inregard to the relationships concerning the variations of the respectivevalues of the molecular weight, the dispersion Mw/Mn, and the particlediameter of the pigment, the same trends apply to the ProductionExamples B2 to B8.

(Evaluation of OD on Regular Papers)

Table 10 shows the evaluation results of printing quality on regularpapers. In Production Example B1, the polymerization conditions(synthesis time and amount of radical polymerization initiator) of thepolymer were adjusted to prepare dispersions with different molecularweights, and these dispersions are compared in the Table. The papersused in these evaluations are the commercially available papers, Xerox4024 paper (made by Xerox USA Corp.), Xerox 10 paper (made by Fuji XeroxCo., Ltd.), Ricopy 6200 paper (made by Ricoh Co., Ltd.), and Epson EPPpaper (made by Seiko Epson Co., Ltd.). The OD values were measured bythe same method as that of Table 3. Results shown in Table 10 were givenwith respect to Production Example B1.

TABLE 10 OD on regular papers according to polymer molecular weight andpigment concentration Polymer molecular weight × 10⁴ 0.51 3.10 5.2310.21 20.13 30.11 Xerox4024 1.40 1.41 1.41 1.42 1.32 1.20 Xerox10 1.411.41 1.39 1.41 1.36 1.15 Ricopy6200 1.32 1.34 1.35 1.36 1.31 1.15 EPP1.42 1.42 1.42 1.43 1.41 1.23

As is clear from the results of Table 10, a high OD is realized by thepolymer having a styrene-equivalent molecular weight as determined bygel permeation chromatography (GPC) of no more than 200000 as in thepresent invention. In regard to the relationships of dispersions usingpolymers of different molecular weights, the same trends apply toProduction Examples B2 to B8.

(Evaluation of the Relationship Between the Amount of BenzylMethacrylate and the OD Value)

Dispersions using polymers (molecular weight: approximately 50000),which were varied in the calculated introduction amounts of benzylmethacrylate, benzyl acrylate, and butyl methacrylate (corresponding to85% of the entire polymer) but otherwise prepared in the same manner asProduction Example B1, were prepared. And the results of evaluation inthe OD on regular paper and the ink storage stability of inks are shownin Table 11. The storage stability is indicated by the percentageincrease of viscosity (%) after 7 days of storage under 70° C. With theexamples shown here, Xerox 4024 paper (made by Xerox USA Corp.) was usedas the regular paper and printing at 720 dpi photo quality using theEM930C, made by Seiko Epson Co., Ltd., was performed. The OD values wereevaluated in the same manner as in the cases of Table 10.

TABLE 11 Benzyl methacrylate/benzyl acrylate amounts and OD (% of addedamount) on regular paper and storage stability Percentage Benzylincrease methacrylate Benzyl acrylate Butyl acrylate OD of viscosity (%)85 0 0 1.35 15.0 80 0 5 1.41 1.2 75 0 20 1.43 1.1 60 0 25 1.45 1.0 45 050 1.42 1.0 40 0 45 1.38 1.0 35 0 50 1.21 1.0 20 0 65 1.15 1.0 15 0 701.05 1.1 0 85 0 1.33 20.5 0 65 20 1.43 1.0 0 60 25 1.43 1.0 0 55 30 1.431.0 0 15 70 1.02 1.2 45 40 0 1.34 1.2 30 30 25 1.45 1.0 20 30 35 1.441.0 10 35 40 1.40 1.1 10 5 70 1.10 1.2

As can be understood from the results of Table 11, the OD value isimproved by using a polymer using benzyl methacrylate and/or benzylacrylate at an amount of 40 to 80% as the polymer for dispersing thepigment. That is, it can be understood that when this amount is lessthan 40%, the coloration on PPC paper or other regular paper degrades,while in the excess of 80%, dispersion stability is not obtained. Thoughthe results for just Production Example B1 are shown for the presentExample, the trends of Table 11 apply likewise to Production Examples B2to B8 and also apply likewise when using other regular papers, such asXerox 10 paper (made by Fuji Xerox Co., Ltd.), Ricopy 6200 paper (madeby Ricoh Co., Ltd.), Epson EPP paper (made by Seiko Epson Co., Ltd.),etc.

(Evaluation of Fixing Property and OD on Specialized Paper)

Table 12 shows results of preparing dispersions using polymers ofdifferent molecular weights, prepared by adjusting the polymerizationconditions (synthesis time and amount of radical polymerizationinitiator) of the polymer in Production Example B1, preparingdispersions using polymers prepared using styrene in place of benzylmethacrylate in Example 1, and evaluating the fixing properties and ODvalues of these dispersions on specialized paper. The OD values wereevaluated by the same method as that of Table 3. The fixing property wasevaluated using specialized paper (PM photo paper) and observing therubbing off of ink when a printed surface and a rear surface areoverlapped with a load of 300 g and moved at a speed of 1m/s. In Table3, AA indicates that there was no rub-off whatsoever even after twotimes of movement, A indicates that though there was no rub-offwhatsoever even after one time of movement, slight rub-off occurredafter two times of movement, B indicates that there was slight rub-off Cindicates that there was rub-off and transfer onto the rear surface, andD indicates that there was considerable rub-off and transfer onto therear surface.

TABLE 12 Fixing property and OD on specialized paper Production Examples(Benzyl methacrylate) Molecular weight × 10⁴ 0.52 3.21 5.41 11.01 19.3332.68 OD 1.8 2.2 2.5 2.6 2.3 2.0 Resistance to rubbing B A AA AA AA BComparative Examples (Styene) Molecular weight × 10⁴ 0.55 3.10 5.2310.21 20.13 30.11 OD 1.7 2.1 2.3 2.5 2.4 1.9 Resistance to rubbing C B AA A C

As is clear from the results of Table 12, the fixing property onspecialized paper is improved and a high OD is realized by the polymerhaving a styrene-equivalent molecular weight as determined by gelpermeation chromatography (GPC) of no less than 20000 and no more than200000, as in the present invention. In regard to the relationships ofdispersions using polymers of different molecular weights, the sametrends apply to Production Examples B2 to B8.

(Evaluation of Discharge Stability)

Table 13 shows the discharge stability evaluation results for the inksof Production Examples B1 to B8 and for variations of Production ExampleB1, wherein the composition was varied to vary the surface tension. Thesurface tension was increased by decreasing the added amounts of OlfinE1010, Olfin STG, Surfynol 61, DEGmBE, TEGmBE, PGmBE, and DPGmBE ofTable 1. The surface tension was lowered by the use of thefluorine-based surfactant Futagent 251 (made by Neos Corp.). Surfacetension measurements were made with the automatic surface tensiometerType CBVP-A3 (made by Kyowa Interface Science Co., Ltd.). For evaluationof the discharge stability, the ink jet printer EM-930C, made by SeikoEpson Co., Ltd., was used to perform continuous printing on 100 pages ofA4-size Xerox P paper at 2000 letters/page of Microsoft Word MS Mingstyle characters of style standard size 10. A indicates that no printdistortions occurred, B indicates that print distortions occurred atless than 10 locations, C indicates that print distortions occurred atno less than 10 locations but less than 100, and D indicates that printdistortions occurred at no less than 100 locations.

TABLE 13 Evaluation results of discharge stability Production SurfaceExample tension Molecular weight × 10⁴ Discharge stability B1 19 5.55 D20 5.55 B 30 0.50 B 30 5.55 A 30 32.10 B 41 5.55 C B2 30 5.24 A B3 315.76 A B4 32 5.55 A B5 30 7.15 A B6 29 5.60 A B7 30 5.56 A B8 31 5.31 A

As can be understood from the results of Table 13, the dischargestability is improved by the polymer having a styrene-equivalentmolecular weight as determined by gel permeation chromatography (GPC) ofno less than 20000 and no more than 200000 and a surface tension of noless than 20 mN/m and no more than 40 mN/m as in the present invention.With regard to the relationships concerning the variation of surfacetension by change of composition, the same trends apply to ProductionExamples B2 to B8.

(Evaluation of Discoloration)

Table 14 shows the results of evaluating the discoloration of ProductionExamples B2, B3, B4, B6, B7, and B8 and dispersions prepared usingpolymers, which were prepared using styrene in place of benzylmethacrylate in these Production Examples (indicated as ComparativeExamples B2, B3, and B4 and Comparative Examples B6, B7, and B8 incorrespondence to the examples). For discoloration, gray patterns (of 3levels differing in OD) were prepared using the cyan ink, magenta ink,and yellow ink of Production Examples B2 to B4, and printed onto Xerox4024 paper and Seiko Epson PM photo paper using the EM930C. The ΔEvalues after leaving the printed matter for 1 year under the conditionsof 30° C. and 45% relative humidity are indicated as the evaluationresults.

TABLE 14 Evaluation results for discoloration Xerox4024 PM photo paperProduction Examples B2, OD 0.31 0.55 0.72 0.42 0.62 0.88 B3, B4 (benzylPercentage change in ΔE 2.2 1.5 1.0 2.1 1.3 0.9 methacrylate) (%)Comparative Examples OD 0.32 0.54 0.74 0.43 0.63 0.90 B2, B3, B4(styrene) Percentage change in ΔE 6.8 4.3 3.3 6.4 4.2 2.8 (%) ProductionExamples B6, OD 0.31 0.55 0.72 0.42 0.62 0.88 B7, B8 (benzyl Percentagechange in ΔE 2.2 1.6 1.2 2.0 1.4 1.0 methacrylate) (%) ComparativeExamples OD 0.32 0.54 0.74 0.43 0.63 0.90 B6, B7, B8 (styrene)Percentage change in ΔE 8.0 6.4 3.4 8.2 6.2 3.1 (%)

As is clear from the results of Table 14, this invention's ink is low indiscoloration. Likewise, the same trends were seen in the case wheregray patterns were prepared using the black ink of Production ExampleB1, with the results were better results. While three colors are used toprepare parts of high lightness and black is used in parts of lowlightness in the gray pattern, a problem of discoloration is seenespecially in the parts of high lightness.

It can thus be understood that an aqueous ink, which is excellent instability, low in blurring and high in coloration on regular paper, andadequate in coloration and provided with fixing property on specializedpaper, can be prepared, and furthermore, in ink jet recording, excellentdischarge stability of the ink from an ink jet head and lowdiscoloration are realized, by the polymer having a styrene-equivalentmolecular weight as determined by gel permeation chromatography (GPC) ofno less than 20000 and no more than 200000 as described above, anaqueous ink, which is excellent in stability, low in blurring and highin coloration on regular paper, and adequate in coloration and providedwith fixing property on specialized paper, can be prepared, andfurthermore, in ink jet recording, excellent discharge stability of theink from an ink jet head and low discoloration are realized.

Example 3

The respective measurement values obtained for this Example weremeasured by the following methods.

(Measurement of the Dispersion of Molecular Weight of the DispersionPolymer)

The molecular weight was measured by taking a part of the synthesizedpolymer and subjecting it to gel permeation chromatography (GPC) usingthe L7100 System made by Hitachi, Ltd., and measuring thestyrene-equivalent number average molecular weight using THF as thesolvent. The dispersion was determined from Mn (number average molecularweight) and Mw (weight average molecular weight), using thestyrene-equivalent number average molecular weight and thestyrene-equivalent weight average molecular weight, determined inlikewise manner.

(Evaluation of dispersion stability)

The Dispersion Stability is Indicated as the Percentage Change inViscosity (%) upon leaving each aqueous ink composition at 60° C. for 30days.

(Measurement of Particle Diameter)

The particle diameter was measured using the Zetasizer 3000HS (made byMalvern Instruments, Inc. (UK)) (light scattering method).

(Measurement of the Percent Change of Viscosity)

For the percentage change in viscosity, viscosity values were measuredat an angle of 60° using the AMVn, made by Anton Paar GmbH, and 1−(valueafter 30 days)/(initial value) is indicated in the form of percentage(%).

(Measurement of OD)

The OD was measured using the Gretag Macbeth Spectroscan SPM-50 (made byGretag Corp.).

(Measurement of Glossiness)

The specular glossiness of a recorded surface was measured for anincidence angle of 60 degrees using a gloss checker (IG-320, made byHoriba, Ltd.) and the average of five measurements was determined foreach recording paper. Specialized paper (PM photo paper, made by SeikoEpson Co., Ltd.) was used as the medium and printing at 720 dpi photoquality using the EM930C, made by Seiko Epson Co., Ltd., as the printerwas performed to prepare the recorded surface.

(Measurement of Surface Tension)

Surface tension was measured with the automatic surface tensiometer TypeCBVP-A3 (made by Kyowa Interface Science Co., Ltd.).

(Evaluation of Discharge Stability)

For Evaluation of the Discharge Stability, Continuous Printing on 100Pages of A4-size Xerox P paper at 2000 letters/page of Microsoft Word MSMing style characters of style standard size 10 were performed with theink jet printer EM-930C, made by Seiko Epson Co., Ltd., and thecircumstances of occurrence of print distortions were observed.

(Evaluation of Fixing Property and OD on Specialized Paper)

The fixing property was evaluated using specialized paper (PM photopaper) and observing the rubbing off of ink when a printed surface and arear surface are overlapped with a load of 300 g and moved at a speed of30 cm/s.

(Measurement of ΔE)

L*, a*, and b* were measured using the Gretag Macbeth Spectroscan SPM-70(made by Gretag Corp.) and ΔE was calculated as the scalar value ofthese measured values.

(Production of Dispersions)

Dispersion C1 Uses Monarch 880 (Made by Cabot Corp.), which is a Carbonblack. After performing nitrogen replacement of the interior of areaction vessel, equipped with a stirrer, thermometer, reflux tube, anddripping funnel, 20 parts of benzyl acrylate, 5 parts of 2-ethylhexylacrylate, 15 parts of butyl acrylate, 10 parts of lauryl acrylate, 2parts of acrylic acid, and 0.3 parts of t-dodecyl mercaptan were placedin the reaction vessel and heated to 70° C. Then 150 parts of benzylacrylate, 15 parts of acrylic acid, 50 parts of butyl acrylate, 1 partof t-dodecyl mercaptan, 20 parts of methyl ethyl ketone, and 1 part ofazobisisobutyronitrile, which were prepared separately, were placed inthe dripping funnel and dripped into the reaction vessel over a periodof 4 hours to carry out a polymerization reaction of a dispersionpolymer. Methyl ethyl ketone was then added to the reaction vessel toprepare a dispersion polymer solution of a concentration of 40%. Thedispersion (Mw/Mn) of the molecular weight was 3.1.

40 parts of the abovementioned dispersion polymer solution, 30 parts ofMonarch 880 (made by Cabot Corp.), which is a carbon black, 100 parts of0.1 mol/L sodium hydroxide aqueous solution, and 30 parts of methylethyl ketone were then mixed and stirred for 30 minutes in ahomogenizer. Thereafter, 300 parts of ion-exchanged water were added andstirring was performed for another hour. The entire amount of methylethyl ketone and a part of the water were then distilled off using arotary evaporator, the pH was adjusted to 9 by neutralization by a 0.1mol/L sodium hydroxide aqueous solution, and filtration through a 0.3 μmmembrane filter was carried out, thereby preparing dispersion C1, havinga solids content (dispersion polymer and carbon black) of 20%.

Dispersion C2 was prepared in the same manner as dispersion C1, exceptusing Pigment Blue 15:3 (copper phthalocyanine pigment; made byClariant, Ltd.) and using cyclohexyl acrylate in place of benzylacrylate in the polymer synthesis method. The value of the molecularweight dispersion (Mw/Mn) was 3.0.

Dispersion C3 was prepared in the same manner as dispersion C1, exceptusing Pigment Red 122 (dimethylquinacridone pigment; made by Clariant,Ltd.) and using cyclohexyl acrylate in place of polymer synthesismethod. The value of the molecular weight dispersion (Mw/Mn) was 3.0.

Dispersion C4 was prepared in the same manner as dispersion C1, exceptusing Pigment Yellow 180 (diketopyrrolopyrrole; made by Clariant, Ltd.)and using cyclohexyl acrylate in place of benzyl acrylate in the polymersynthesis method. The value of the molecular weight dispersion (Mw/Mn)was 3.5.

Dispersion C5 was prepared in the same manner as dispersion C1, exceptusing a mixture of 50% benzyl acrylate and 50% isobornyl acrylate inplace of the benzyl acrylate in dispersion C1 and using Leben C (made byColumbian Carbon Ltd.), which is a carbon black. The value of themolecular weight dispersion (Mw/Mn) was 3.5.

Dispersion C6 was prepared in the same manner as dispersion C5, exceptusing Pigment Blue 15:3 (copper phthalocyanine pigment; made byClariant, Ltd.) and using a mixture of 50% cyclohexyl acrylate and 50%isobornyl acrylate in place of the mixture of 50% benzyl acrylate and50% isobornyl acrylate in the polymer synthesis method. The value of themolecular weight dispersion (Mw/Mn) was 3.0.

Dispersion C7 was prepared in the same manner as dispersion C5, exceptusing Pigment Red 122 (dimethylquinacridone pigment; made by Clariant,Ltd.) and using a mixture of 50% cyclohexyl acrylate and 50% isobornylacrylate in place of the mixture of 50% benzyl acrylate and 50%isobornyl acrylate in the polymer synthesis method. The value of themolecular weight dispersion (Mw/Mn) was 3.0.

Dispersion C8 was prepared in the same manner as dispersion C5, exceptusing Pigment Yellow 180 (diketopyrrolopyrrole; made by Clariant, Ltd.)and using a mixture of 50% cyclohexyl acrylate and 50% isobornylacrylate in place of the mixture of 50% benzyl acrylate and 50%isobornyl acrylate in the polymer synthesis method. The value of themolecular weight dispersion (Mw/Mn) was 3.5.

For each of dispersions C2 to C8, the weight ratio of the dispersionpolymer to the pigment was adjusted to 20:80.

(Preparation of Ink Jet Inks)

Favorable examples of compositions as ink jet recording ink areindicated below in Table 15, as specific examples of aqueous ink. InTable 15, the added amount of dispersion is indicated with the amountthereof (solids concentration: total amount of pigment and dispersionpolymer) converted to weight. 0.05% Topside 240 (made by Permachem AsiaLtd.) in ion-exchanged water for prevention of corrosion of ink, 0.02%benzotriazole in ion-exchanged water for prevention of corrosion of inkjet head parts, and 0.04% EDTA (ethylenediamine tetraacetic acid) 2Nasalt in ion-exchanged water for reducing the effects of metal ions inthe ink system were used in the residual quantity of water in each ofthe Examples.

TABLE 15 Ink compositions Production Examples C1 C2 C3 C4 C5 C6 C7 C8Dispersion C1 7.5 — — — — — — — Dispersion C2 — 4 — — — — — — DispersionC3 — — 6.5 — — — — — Dispersion C4 — — — 6 — — — — Dispersion C5 — — — —8 — — — Dispersion C6 — — — — — 5 — — Dispersion C7 — — — — — — 6 —Dispersion C8 — — — — — — — 8 TEGmBE 2 1 1 1 2 1 1 1 1,2-hexanediol 3 44 4 3 4 4 4 Glycerin 10 15 10 10 10 13 10 7 Trimethylolpropane 4 7 5 5 47 5 5 Surfynol 104 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Ion-exchanged waterResidual Residual Residual Residual Residual Residual Residual Residualquantity quantity quantity quantity quantity quantity quantity quantityTEGmBE: triethylene glycol monobutyl ether

(Evaluation of Dispersion Stability)

The aqueous ink prepared by the above-described methods were left for 30days at 60° C., and the values of percentage change in viscosity (%) areshown. A lower percentage change in viscosity indicates a higherstability. Results are shown for the inks of Production Examples C1 toC8 and for variations of Production Example C1, in which the polymersynthesis method (synthesis time and amount of radical polymerizationinitiator) was varied to vary the respective values of average molecularweight and the dispersion Mw/Mn, as well as for variations of ProductionExample C1 in which the particle diameter of the pigment was varied. Forvariation of the molecular weight dispersion Mw/Mn, a plurality of typesof polymers of different molecular weights were mixed and used. Theresults are shown in Table 16. The molecular weights shown in Table 16are number average molecular weights.

TABLE 16 Measurement results of percentage change in viscosityPercentage Production Molecular Particle change in Example weight × 10⁴Mw/Mn diameter (nm) viscosity (%) C1 0.51 3.1 100 1.4 1.12 3.1 100 1.23.10 3.1 100 1.0 5.23 3.1 100 1.0 10.21 1.3 100 1.2 10.21 2.2 100 1.010.21 3.1 100 1.0 10.21 3.1 15 13.2 10.21 3.2 20 1.0 10.21 5.3 300 1.810.21 10.5 100 1.0 10.21 11.3 100 1.2 20.13 3.1 100 2.4 25.20 3.1 1003.5 30.11 3.1 100 8.1 C2 5.62 3.0 90 1.0 C3 5.96 3.0 95 1.0 C4 5.82 3.5100 1.0 C5 7.35 3.5 100 1.0 C6 7.58 3.0 90 1.0 C7 4.24 3.0 95 1.0 C86.13 3.5 100 1.0

(Evaluation of OD on Regular Papers)

In Production Example C1, the conditions of polymerization (synthesistime and amount of radical polymerization initiator) of the polymer wereadjusted to prepare dispersions with polymers of different molecularweights. Dispersions using the same pigment as that of Example 1, acommercially available acrylic styrene dispersion polymer, and aluminabeads and dispersed using an Eiger mill, were also prepared. Acomparison between these dispersions is shown. A higher OD valueindicates a better result. The papers used in these evaluations werecommercially available regular papers, such as Xerox 4024 paper (made byXerox USA Corp.), Xerox 10 paper (made by Fuji Xerox Co., Ltd.), Ricopy6200 paper (made by Ricoh Co., Ltd.), and Epson EPP paper (made by SeikoEpson Co., Ltd.). Table 17 shows the evaluation results of the printingquality on these regular papers. These results clearly show thatpreferable OD values on regular paper are obtained by phase inversionemulsification, regardless of the type of regular paper. Also, thenumber average molecular weight is preferably no less than 5000 and nomore than 200000, more preferably no less than 20000 and no more than100000.

TABLE 17 Polymer molecular weight and OD on regular papers MolecularDispersion weight × method 10⁴ Xerox4024 Xerox10 Ricopy6200 EPP Phase0.51 1.40 1.41 1.32 1.42 inversion 3.10 1.41 1.41 1.34 1.42 emul- 5.231.41 1.39 1.35 1.42 sification 10.21 1.42 1.41 1.36 1.43 20.13 1.32 1.361.31 1.41 30.11 1.20 1.15 1.15 1.23 30.11 1.20 1.15 1.15 1.23 Eiger mill3.20 1.01 1.00 0.95 1.02 10.61 0.98 0.95 0.94 1.00

(Evaluation of the Relationship Between the Amount of Acrylate and Glosson Specialized Paper)

The dispersion polymers of Production Example C1 were partially changedfrom benzyl acrylate, 2-ethylhexyl acrylate, butyl acrylate, laurylacrylate, and acrylic acid, each of which is a component comprising anacrylate or acrylic acid, to benzyl methacrylate, 2-ethylhexylmethacrylate, butyl methacrylate, lauryl methacrylate, and methacrylicacid, each of which is a component comprising a methacrylate ormethacrylic acid. And the changes in the gloss of printed matter printedonto specialized paper (PM photo paper, made by Seiko Epson Co., Ltd.)were evaluated for these dispersions. These Production Examples areindicated as C11 to C19. The added amounts shown here are loadingweights (weight %) of the monomers. A higher glossiness indicates abetter result. From these results, it can be understood that favorableglossiness can be obtained when the acrylic amount is no less than 80%.

TABLE 18 Results of measurement of gloss for cases where the dispersionpolymers are changed from components comprising an acrylate or acrylicacid to components comprising a methacrylate or methacrylic acid Polymercomposition C11 C12 C13 C14 C15 C16 C17 C18 C19 BZA 50 50 50 40 30 0 040 0 2EHA 20 0 10 0 10 0 0 0 10 BA 10 20 10 30 20 0 10 0 0 LA 10 10 0 1010 0 0 0 0 AA 10 10 10 10 10 0 0 0 5 BZMA 0 0 0 10 0 50 50 30 30 2EHMA 00 20 0 0 20 0 10 20 BMA 0 0 0 0 0 8 18 8 9 LMA 0 10 0 0 0 10 10 0 0 MA 00 0 0 0 12 12 12 6 ST 0 0 0 0 20 0 0 0 20 Mn¹⁾ 10000 20000 25000 3100025000 3000 26000 31000 8000 Mw²⁾ 31000 76000 71000 105000 79000 9300070000 100000 25000 Mw/Mn 3.1 3.8 2.8 3.4 3.2 3.1 2.7 3.2 3.1 Acrylic 10090 80 100 80 0 10 40 15 amount³⁾ Glossiness 78 70 65 75 65 35 30 45 40¹⁾Mn: number average molecular weight ²⁾Mw: weight average molecularweight ³⁾Acrylic amount: total amount of acrylic acid and acrylates (%)

Benzyl acrylate (BZA)

2-ethylhexyl acrylate (2EHA)

Butyl acrylate (BA)

Lauryl acrylate (LA)

Acrylic acid (AA)

Benzyl methacrylate (BZMA)

2-ethylhexyl methacrylate (2EHMA)

Butyl methacrylate (BMA)

Lauryl methacrylate (LMA)

Methacrylic acid (MA)

Styrene (ST)

(Evaluation of Fixing Property and OD on Specialized Paper)

In Production Example C1, the conditions of polymerization (synthesistime and amount of azobisisovaleronitrile, which is a radicalpolymerization initiator) of the polymer were adjusted to preparedispersions with polymers of different number average molecular weights.Dispersions, using polymers with which the benzyl methacrylate inProduction Example C1 was changed to styrene, were also prepared. Table19 shows the results of evaluating the fixing properties and OD valuesof these dispersions on specialized. The OD values were evaluated by thesame method as that of the cases shown in Table 17. The molecularweights shown in Table 19 are number average molecular weights. In Table19, AA indicates that there was no rub-off whatsoever even after twotimes of movement, A indicates that though there was no rub-offwhatsoever even after one time of movement, slight rub-off occurredafter two times of movement, B indicates that there was slight rub-off,C indicates that there was rub-off and transfer onto the rear surface,and D indicates that there was considerable rub-off and transfer ontothe rear surface. It is clear from Table 19, that when due to thecontaining of styrene, the total amount of acrylic acid and acrylatesbecomes less than 80%, the fixing property will not be excellent as awhole when the water dispersible polymer is used. It is also clear thatthe molecular weight of the polymer is preferably no less than 5000,more preferably no less than 10000, and even more preferably no lessthan 20000. Yet even more preferably, the polymer molecular weight is noless than 30000. Also, the polymer molecular weight is preferably nomore than 300000 and more preferably no more than 200000.

TABLE 19 Fixing property and OD on specialized paper Dispersions usingpolymers of different molecular weights in Production Example C1Molecular weight × 10⁴ 0.52 3.21 5.41 11.01 19.33 32.68 OD 1.8 2.2 2.52.6 2.3 2.0 Resistance to rubbing B A AA AA AA B Dispersions in whichstyrene was used in place of the benzyl methacrylate in ProductionExample C1 Molecular weight × 10⁴ 0.55 3.10 5.23 10.21 20.13 30.11 OD1.7 2.1 2.3 2.5 2.4 1.9 Resistance to rubbing C B A A A C

(Evaluation of Discoloration 1)

Polymers using styrene in place of benzyl acrylate in ProductionExamples C2, C3, and C4, were used to prepare Dispersions (ComparativeExamples C1, C2, and C3), and these were evaluated for discoloration.Comparative Examples C1, C2, and C3 were prepared in the same manner asProduction Examples C2, C3, and C4, respectively, except using styrenein place of benzyl acrylate.

Polymers using styrene in place of benzyl acrylate in ProductionExamples C6, C7, and C8, were used to prepare dispersions (ComparativeExamples C4, C5, and C6), and these were evaluated for discoloration.Comparative Examples C4, C5, and C6 were prepared in the same manner asProduction Examples C6, C7, and C8 respectively, except using styrene inplace of benzyl acrylate.

For discoloration, gray patterns (of 3 levels differing in OD) wereprepared using the cyan ink, magenta ink, and yellow ink of ProductionExamples C2 to C4 and Production Examples C6 to C8 (Comparative ExamplesC1 to C3 and Comparative Examples C4 to C6) and printed onto Xerox 4024paper and Seiko Epson PM photo paper using the EM930C. The values of thecolor difference (ΔE) after leaving for 1 year under the conditions of30° C. and 45% relative humidity are indicated as the evaluation resultsin Table 20 below. A smaller color difference indicates a better result.

TABLE 20 Evaluation results of discoloration Xerox4024 PM photo paperProduction Examples OD 0.31 0.55 0.72 0.42 0.62 0.88 C2, C3, C4 (benzylPercentage change in ΔE 2.2 1.5 1.0 2.1 1.3 0.9 acrylate) (%)Comparative Examples OD 0.32 0.54 0.74 0.43 0.63 0.90 C1, C2, C3(styrene) Percentage change in ΔE 6.8 4.3 3.3 6.4 4.2 2.8 (%) ProductionExamples OD 0.31 0.55 0.72 0.42 0.62 0.88 C6, C7, C8 (benzyl Percentagechange in ΔE 2.2 1.6 1.2 2.0 1.4 1.0 acrylate) (%) Comparative ExamplesOD 0.32 0.54 0.74 0.43 0.63 0.90 C4, C5, C6 (styrene) Percentage changein ΔE 8.0 6.4 3.4 8.2 6.2 3.1 (%)

It is clear from Table 20 that a significantly low discoloration can besecured by using a water-dispersible polymer, with which the totalamount of acrylic acid and acrylates is made less than 80% as a resultof having styrene as a monomer component. Also, this low discolorationis obtained regardless of the type of recording medium.

Example 4

The respective measurement values obtained for this Example weremeasured by the following methods.

(Measurement of the Refractive Index of the Dispersion Polymer)

The solvent and water were eliminated from the synthesized dispersionpolymer to form a film-like sample and this was measured with the Abbe'srefractometer, 3T.

(Sedimentation Percentage)

The sedimentation percentage is obtained from the peak value (fixed at500 nm in the case of carbon black), which is obtained by placing a1000-times diluted solution of the ink in a 1 cm cell and making ameasurement in the range of 300 nm to 800 nm using the UV-visiblespectrophotometer, U3300, made by Hitachi, Ltd., and is the valueobtained by 1−(the absorbance after leaving still for 6 months in theink state/the initial absorbance) and expressed in %.

(Evaluation of Fixing Property on Specialized Paper)

The fixing property was evaluated using specialized paper (PM photopaper) and observing the rubbing off of ink when a printed surface and arear surface are overlapped with a load of 300 g and moved at a speed of1m/s.

The measurement of the molecular weight of each dispersion polymer,evaluation of the dispersion stability, measurement of the particlediameter, measurement of the percentage change in viscosity, measurementof OD, and measurement of glossiness were carried out by the samemethods as those of Example 3.

(Production of Dispersions)

Dispersion D1 uses Monarch 880 (made by Cabot Corp.), which is a carbonblack. After performing nitrogen replacement of the interior of areaction vessel, equipped with a stirrer, thermometer, reflux tube, anddripping funnel, 65 parts of paracumylphenoxyethylene glycol acrylate,10 parts of benzyl acrylate, 2 parts of acrylic acid, and 0.3 parts oft-dodecyl mercaptan were placed in the reaction vessel and heated to 70°C. Then 150 parts of paracumylphenoxyethylene glycol acrylate, 15 partsof acrylic acid, 5 parts of butyl acrylate, 1 part of t-dodecylmercaptan, 20 parts of methyl ethyl ketone, and 1 part ofazobisisobutyronitrile, which were prepared separately, were placed inthe dripping funnel and dripped into the reaction vessel over a periodof 4 hours to carry out a polymerization reaction of a dispersionpolymer. Methyl ethyl ketone was then added to the reaction vessel toprepare a dispersion polymer solution of a concentration of 40%.

40 parts of the abovementioned dispersion polymer solution, 30 parts ofMonarch 880 (made by Cabot Corp.), which is a carbon black, 100 parts of0.1 mol/L sodium hydroxide aqueous solution, and 30 parts of methylethyl ketone were then mixed and stirred for 30 minutes in ahomogenizer. Thereafter, 300 parts of ion-exchanged water were added andstirring was performed for another hour. The entire amount of methylethyl ketone and a part of the water were then distilled off using arotary evaporator, the pH was adjusted to 9 by neutralization by a 0.1mol/L sodium hydroxide aqueous solution, and filtration through a 0.3 μmmembrane filter was carried out, thereby preparing dispersion D1. Thepolymer thus obtained had the refractive index of 1.55.

Dispersions D2 to D4 were obtained by the same method as the above.Dispersion D2 was prepared using Pigment Blue 15:3 (copperphthalocyanine pigment made by Clariant, Ltd.) and adjusting the weightratio of the pigment to polymer to 55:45. Dispersion D3 was preparedusing Pigment Red 122 (dimethylquinacridone pigment; made by Clariant,Ltd.) and adjusting the weight ratio of the pigment to polymer to 75:25.Dispersion D4 was prepared using Pigment Yellow 180(diketopyrrolopyrrole; made by Clariant, Ltd.) and adjusting the weightratio of the pigment to polymer to 75:25.

(Preparation of Ink Jet Inks)

Favorable examples of compositions as ink jet recording ink areindicated below in Table 21, as specific examples of aqueous ink.

TABLE 21 Ink compositions Production Examples D1 D2 D3 D4 Dispersion D18 — — — Dispersion D2 — 7 — — Dispersion D3 — — 8 — Dispersion D4 — — —8 TEGmBE 2 1 1 1 1,2-hexanediol 3 4 4 4 Glycerin 10 15 10 10Trimethylolpropane 4 7 5 5 Surfynol 104 0.1 0.1 0.1 0.1 Ion-exchangedwater Residual Residual Residual Residual quantity quantity quantityquantity TEGmBE: triethylene glycol monobutyl ether Surfynol 104:acetylene glycol surfactant, made by Nissin Chemical Industry Co., Ltd.

In Table 21, the added amount of dispersion is indicated with the amountthereof (solids concentration: total amount of pigment and dispersionpolymer) converted to weight. 0.05% Topside 240 (made by Permachem AsiaLtd.) in ion-exchanged water for prevention of corrosion of ink, 0.02%benzotriazole in ion-exchanged water for prevention of corrosion of inkjet head parts, and 0.04% EDTA (ethylenediamine tetraacetic acid) 2Nasalt in ion-exchanged water for reducing the effects of metal ions inthe ink system were used in the residual quantity of water in each ofthe Examples.

(Evaluation of the Refractive Indices of Dispersion Polymers andEvaluation of OD on Regular Paper and Glossiness on Glossy Paper)

After synthesizing polymers with different refractive index, by changingtypes of monomers used therein, and dispersions were prepared in thesame manners as described above with these polymers. Table 22 shows theevaluation results of OD on regular paper and glossiness on glossypaper, with respect to these dispersions. In addition to polymer I whichuses paracumylphenoxyethylene glycol acrylate as in the present Example,polymer II which uses lauryl acrylate in place ofparacumylphenoxyethylene glycol acrylate, and polymer III which uses2-ethylhexyl acrylate in place of paracumylphenoxyethylene glycolacrylate were prepared in the same manner and with the other componentsbeing the same as dispersions D1 to D4, and inks were prepared usingthese dispersions in the same manner as the corresponding ProductionExamples.

Xerox 4024 paper (made by Xerox USA Corp.) was used as the regular paperand PM photo paper (made by Seiko Epson Co., Ltd.) was used as theglossy paper. The EM930C, made by Seiko Epson Co., Ltd., was used as theprinter and evaluations were made using samples printed at 720 dpi photoquality in the case of the regular paper and samples printed at 1440 dpiphoto quality in the case of the glossy paper.

TABLE 22 Refractive index of dispersion polymer and OD on regular paperand glossiness on glossy paper Glossiness Production DispersionRefractive index of OD on on Example polymer dispersion polymer regularpaper glossy paper D1 I 1.55 1.45 70 II 1.44 1.37 45 III 1.46 1.39 48 D2I 1.55 1.25 80 II 1.44 1.18 50 III 1.46 1.18 51 D3 I 1.55 1.25 81 II1.44 1.15 49 III 1.46 1.15 52 D4 I 1.55 1.3 80 II 1.44 1.18 46 III 1.461.19 54

As shown in Table 22, with all Production Examples usingparacumylphenoxyethylene glycol acrylate, the refractive index was noless than 1.50 and both OD on regular paper and glossiness on glossypaper were excellent. In contrast, with all Production Examples usinglauryl acrylate or 2-ethylhexyl acrylate in place ofparacumylphenoxyethylene glycol acrylate, the refractive index was lessthan 1.50 and both OD on regular paper and glossiness on glossy paperwere clearly poorer in comparison to the Production Examples usingparacumylphenoxyethylene glycol acrylate. From the above, it is clearthat a refractive index of no less than 1.50 is preferable and that apolymer with such a refractive index can be obtained as a copolymer ofparacumylphenoxyethylene glycol acrylate and another acrylate or acrylicacid.

(Evaluation of Pigment Particle Diameter and Dispersion Stability)

Dispersions which differ in the particle diameter of the pigment wereprepared in the same manner as described above and using thesedispersions, inks were prepared in the same manner as the correspondingProduction Examples. The percentage change in viscosity (%) andsedimentation percentage (%) upon leaving these inks at 60° C. for 30days are shown in Table 23. It is clear from Table 23 that the pigmentparticle diameter is preferably no less than 20 nm and no more than 150nm and preferably no less than 30 nm and no more than 100 nm.

TABLE 23 Evaluation of pigment particle diameter and dispersionstability Production Pigment particle Percentage change SedimentationExample diameter (nm) of viscosity (%) percentage (%) D1 80 0.2 4.3 1000.1 5.8 60 0.5 3.3 15 18.3 1.8 150 0.2 15.5 D2 70 0.2 4.1 90 0.2 5.4 600.1 3 16 11 15 150 0.1 20.2 D3 80 0.5 4.1 90 0.7 5.4 60 0.4 3 18 21.41.5 150 0.4 18.7 D4 80 0.4 4.1 90 0.5 5.4 60 0.2 3 19 10.3 1.5 180 0.216.9

(Evaluation of Polymer Molecular Weight and Fixing Property on GlossyPaper)

Dispersions, using polymers of different molecular weights, wereprepared by adjusting the polymerization conditions (synthesis time,amount of radical polymerization initiator, and reaction time) of thedispersion polymer in Production Example D1, and dispersions, usingpolymers with which the paracumylphenoxyethylene glycol acrylate inProduction Example D1 is partially changed to another acrylate ormethacrylate, were prepared and inks were prepared using thesedispersions in the same manner as the corresponding Production Example.Table 24 shows the results of evaluation of fixing property onspecialized paper using these inks.

TABLE 24 Evaluation of fixing property on glossy paper ProductionDispersion Molecular Fixing property Example polymer weight × 10⁴ onglossy paper D1 I 0.41 C I 1.12 B I 3.1 A I 1023 A I 19.81 B II 6.11 CIII 5.25 C IV 8.57 D I 20.13 Could not be dispersed.

The fixing property was evaluated visually. In Table 24, A indicatesthat there was no rub-off whatsoever even after two times of movement, Bindicates that though there was no rub-off whatsoever even after onetime of movement, slight rub-off occurred after two times of movement, Cindicates that there was slight rub-off, and D indicates that there wasrub-off. Dispersion polymers I, II, and III are the same as those ofTable 22, and with dispersion polymer IV, 2-ethylhexyl methacrylate wasused in place of paracumylphenoxyethylene glycol acrylate. The othercomponents were the same and synthesis was performed in the same manneras in the present Example in this case as well. The sample with whichthe molecular weight exceeded 200000 was difficult to disperse and couldnot be evaluated. The viscosity of the dispersion tended to increasewhen the molecular weight exceeded 100000.

Example 5

The respective measurement values obtained for this Example weremeasured by the following methods.

(Measurement of the Sulfur Content in a Polymer)

Each synthesized dispersion polymer was subject to elemental analysisusing the 2400CHN Elemental Analyzer (made by Perkin Elmer Inc. (USA))to measure the weight % of sulfur.

The measurement of the molecular weight of each dispersion polymer,evaluation of the dispersion stability, measurement of the particlediameter, measurement of the percentage change in viscosity, measurementof OD, and measurement of glossiness were carried out by the samemethods as those of Example 3, and the measurement of the refractiveindex of each dispersion polymer, the evaluation of the sedimentationpercentage, and the evaluation of fixing property on specialized paperwere carried out by the same methods as those of Example 4.

(Production of Dispersions)

Dispersion E1 uses Monarch 880 (made by Cabot Corp.), which is a carbonblack. After performing nitrogen replacement of the interior of areaction vessel, equipped with a stirrer, thermometer, reflux tube, anddripping funnel, 25 parts of phenyl thiomethacrylate, 20 parts of benzylacrylate, 2 parts of acrylic acid, and 0.3 parts of t-dodecyl mercaptanwere placed in the reaction vessel and heated to 80° C. Then 50 parts ofphenyl thiomethacrylate, 40 parts of benzyl acrylate, 15 parts ofacrylic acid, 5 parts of butyl acrylate, 1 part of t-dodecyl mercaptan,20 parts of methyl ethyl ketone, and 1 part of azobisisobutyronitrile,which were prepared separately, were placed in the dripping funnel anddripped into the reaction vessel over a period of 4 hours to carry out apolymerization reaction of a dispersion polymer. Methyl ethyl ketone wasthen added to the reaction vessel to prepare a dispersion polymersolution of a concentration of 40%.

40 parts of the abovementioned dispersion polymer solution, 30 parts ofMonarch 880 (made by Cabot Corp.), which is a carbon black, 100 parts of0.1 mol/L sodium hydroxide aqueous solution, and 30 parts of methylethyl ketone were then mixed and stirred for 30 minutes in ahomogenizer. Thereafter, 300 parts of ion-exchanged water were added andstirring was performed for another hour. The entire amount of methylethyl ketone and a part of the water were then distilled off using arotary evaporator, the pH was adjusted to 9 by neutralization by a 0.1mol/L sodium hydroxide aqueous solution, and filtration through a 0.3 μmmembrane filter was carried out, thereby preparing dispersion E1. Thepolymer thus obtained had the refractive index of 1.58.

Dispersions E2 to E4 were obtained by the same method as the above.Dispersion E2 was prepared using Pigment Blue 15:4 (copperphthalocyanine pigment; made by Clariant, Ltd.) and adjusting the weightratio of the pigment to polymer to 55:45. Dispersion E3 was preparedusing Pigment Red 122 (dimethylquinacridone pigment; made by Clariant,Ltd.) and adjusting the weight ratio of the pigment to polymer to 75:25.Dispersion E4 was prepared using Pigment Yellow 74 (condensed azopigment; made by Clariant, Ltd.) and adjusting the weight ratio of thepigment to polymer to 75:25.

(Preparation of Ink Jet Inks)

Favorable examples of compositions as ink jet recording ink areindicated below in Table 25, as specific examples of aqueous ink. InTable 25, the added amount of dispersion is indicated with the amountthereof (solids concentration: total amount of pigment and dispersionpolymer) converted to weight. 0.05% Topside 240 (made by Permachem AsiaLtd.) in ion-exchanged water for prevention of corrosion of ink, 0.02%benzotriazole in ion-exchanged water for prevention of corrosion of inkjet head parts, and 0.04% EDTA (ethylenediamine tetraacetic acid) 2Nasalt in ion-exchanged water for reducing the effects of metal ions inthe ink system were used in the residual quantity of water in each ofthe Examples.

TABLE 25 Ink compositions Production Examples E1 E2 E3 E4 Dispersion E18.5 — — — Dispersion E2 — 7.5 — — Dispersion E3 — — 8 — Dispersion E4 —— — 8 TEGmBE 2 1 1 1 1,2-hexanediol 3 4 4 4 Glycerin 10 15 10 10Trimethylolpropane 4 7 5 5 Surfynol 104 0.1 0.1 0.1 0.1 Ion-exchangedwater Residual Residual Residual Residual quantity quantity quantityquantity TEGmBE: triethylene glycol monobutyl ether Surfynol 104:acetylene glycol surfactant, made by Nissin Chemical Industry Co., Ltd.

(Evaluation of the Refractive Indices of Dispersion Polymers andEvaluation of OD on Regular Paper and Glossiness on Glossy Paper)

After synthesizing polymers with different refractive index, by changingtypes of monomers used therein, and dispersions were prepared in thesame manners as described above with these polymers. Table 26 shows theevaluation results of OD on regular paper and glossiness on glossypaper, with respect to these dispersions. In addition to polymer I whichuses phenyl thiomethacrylate as in the present Example, polymer II whichuses lauryl acrylate in place of phenyl thiomethacrylate, and polymerIII which uses 2-ethylhexyl acrylate in place of phenylthiomethacrylate, were prepared in the same manner and with the othercomponents being the same as dispersions E1 to E4, and inks wereprepared using these dispersions in the same manner as the correspondingProduction Examples.

Xerox 4024 paper (made by Xerox USA Corp.) was used as the regular paperand PM photo paper (made by Seiko Epson Co., Ltd.) was used as theglossy paper. The EM930C, made by Seiko Epson Co., Ltd., was used as theprinter and evaluations were made using samples printed at 720 dpi photoquality in the case of the regular paper and samples printed at 1440 dpiphoto quality in the case of the glossy paper.

TABLE 26 Refractive index of dispersion polymer and OD on regular paperand glossiness on glossy paper Glossiness Production DispersionRefractive index of OD on on Example polymer dispersion polymer regularpaper glossy paper E1 I 1.58 1.46 74 II 1.45 1.36 47 III 1.47 1.38 49 E2I 1.58 1.27 83 II 1.45 1.17 51 III 1.47 1.17 53 E3 I 1.58 1.28 85 II1.45 1.15 51 III 1.47 1.14 53 E4 I 1.58 1.33 84 II 1.45 1.16 48 III 1.471.17 56

As shown in Table 26, with all Production Examples using phenylthiomethacrylate, the refractive index was no less than 1.50 and both ODon regular paper and glossiness on glossy paper were excellent. Incontrast, with all Production Examples using lauryl acrylate or2-ethylhexyl acrylate in place of phenyl thiomethacrylate, therefractive index was less than 1.50 and both OD on regular paper andglossiness on glossy paper were clearly poorer in comparison to theProduction Examples using phenyl thiomethacrylate. From the above, it isclear that a refractive index of no less than 1.50 is preferable, andthat a polymer with such a refractive index can be obtained as acopolymer of phenyl thiomethacrylate and another acrylate or acrylicacid.

(Evaluation of Pigment Particle Diameter and Dispersion Stability)

Dispersions which differ in the particle diameter of the pigment wereprepared in the same manner as described above and using thesedispersions, inks were prepared in the same manner as the correspondingProduction Examples. The percentage change in viscosity (%) andsedimentation percentage (%) upon leaving these inks at 60° C. for 30days are shown in Table 27.

TABLE 27 Evaluation of pigment particle diameter and dispersionstability Production Pigment particle Percentage change SedimentationExample diameter (nm) of viscosity (%) percentage (%) E1 80 0.1 4.2 1000.1 5.7 60 0.3 3.2 15 17.3 1.7 150 0.1 17.3 E2 70 0.2 4.3 90 0.2 5.5 600.2 3.2 16 12.1 1.6 150 0.1 22.2 E3 80 0.4 4.6 90 0.6 5.4 60 0.3 3.5 1820.4 1.5 150 0.3 19.7 E4 80 0.3 4.3 90 0.4 5.6 60 0.2 3.5 19 11.5 1.4180 0.2 17.4

It is clear from Table 27 that the pigment particle diameter ispreferably no less than 20 nm and no more than 150 nm and preferably noless than 30 nm and no more than 100 nm.

(Evaluation of Polymer Molecular Weight and Fixing Property on GlossyPaper)

Dispersions, using polymers of different molecular weights, wereprepared by adjusting the polymerization conditions (synthesis time,amount of radical polymerization initiator, and reaction time) of thedispersion polymer in Production Example E1, and dispersions, usingpolymers with which the phenyl thiomethacrylate in ink compositionexample 1 was partially changed to another acrylate or methacrylate,were prepared, and inks were prepared using these dispersions in thesame manner as the corresponding Production Example. The results ofevaluation of fixing property on specialized paper using these inks areshown in Table 28. The fixing property was evaluated visually. In Table28, A indicates that there was no rub-off whatsoever even after twotimes of movement, B indicates that though there was no rub-offwhatsoever even after one time of movement, slight rub-off occurredafter two times of movement, C indicates that there was slight rub-offand D indicates that there was rub-off. When a monomer other thanparacumylphenoxyethylene glycol acrylate was used, adequate fixingproperty on glossy paper became difficult to obtain.

TABLE 28 Evaluation of fixing property on glossy paper ProductionDispersion Molecular Fixing property Example polymer weight × 10⁴ onglossy paper E1 I 0.44 C I 1.22 B I 3.5 A I 10.89 A I 19.85 B II 6.15 CIII 5.35 C IV 8.24 D I 21.37 Could not be dispersed.

Dispersion polymers I, II, and III are the same as those of Table 26,and with dispersion polymer IV, 2-ethylhexyl methacrylate was used inplace of phenyl thiomethacrylate. The other components were the same,synthesis was performed in the same manner as in dispersion E1, and anink was prepared using the synthesized dispersion in the same manner asthe corresponding Production Example in this case as well. The samplewith which the molecular weight exceeded 200000 was difficult todisperse and could not be evaluated. The viscosity of the dispersiontended to increase when the molecular weight exceeded 100000. Themolecular weight is preferably no less than 10000, more preferably noless than 20000 or no less than and 30000, and preferably no more than100000.

Example 6 Production of Dispersions

Monarch 880 (made by Cabot Corp.), which is a carbon black, was used asthe pigment in dispersion F1. After performing nitrogen replacement ofthe interior of a reaction vessel, equipped with a stirrer, thermometer,reflux tube, and dripping funnel, the monomer composition shown in Table1 and 20 parts of benzyl acrylate, 15 parts of 2-ethylhexyl acrylate, 15parts of butyl acrylate, 10 parts of lauryl acrylate, 2 parts of acrylicacid, and 0.3 parts of t-dodecyl mercaptan were placed in the reactionvessel and heated to 70° C., and then 50 parts of benzyl acrylate, 15parts of 2-ethylhexyl acrylate, 15 parts of acrylic acid, 50 parts ofthe urethane acrylate, CN961 (made by Nippon Kayaku Co., Ltd.), 1 partof t-dodecyl mercaptan, 120 parts of methyl ethyl ketone, and 1 part ofazobisisovaleronitrile, which were prepared separately, were placed inthe dripping funnel and dripped into the reaction vessel over a periodof 4 hours to carry out a polymerization reaction of a polymer. Methylethyl ketone was then added to the reaction vessel to prepare a polymersolution of a concentration of 40%. The molecular weight dispersion(Mw/Mn) of the polymer was 3.1, and the styrene-equivalent numberaverage molecular weight was 10.21×10⁴. The content of the urethanebonds, urea bonds, allophanate bonds, and biuret bonds at this point was1.0 mmol/g.

The molecular weight of the polymer was determined by the methoddescribed for Example 3 and the quantification of the urethane bonds,etc., was carried out by the following method.

(Measurement of the Urethane Bonds, Urea Bonds, Allophanate Bonds, andBiuret Bonds)

An excess amount of n-butylamine was added to the synthesized polymer,and after leaving at 40° C. for 24 hours, back titration using an HClsolution of 0.1% concentration was performed to cut the crosslinkingallophanate and biuret groups. This amine-treated polymer, including theurethane and urea produced as a result of decomposition by the amine,was measured by GC-MS and the total amount and respective amounts ofurethane bonds, urea bonds, allophanate bonds, and biuret bonds werecalculated.

40 parts of the abovementioned polymer solution, 30 parts of Monarch 880(made by Cabot Corp.), 100 parts of 0.1 mol/L sodium hydroxide aqueoussolution, and 30 parts of methyl ethyl ketone were then mixed andstirred for 30 minutes in a homogenizer. Thereafter, 300 parts ofion-exchanged water were added and stirring was performed for anotherhour. The entire amount of methyl ethyl ketone and a part of the waterwere then distilled off using a rotary evaporator, the pH was adjustedto 9 by neutralization by a 0.1 mol/L sodium hydroxide aqueous solution,and filtration through a 0.3 μm membrane filter was carried out, therebypreparing dispersion F1 (containing a polymer-coated pigment), having asolids content (dispersion polymer and carbon black) of 20%. DispersionsF2 to F4 were obtained by the same method as the above. Each dispersionwas prepared so that the weight ratio of the dispersion polymer and thepigment will be 20:80. Table 29 shows the synthesis components and thevarious measurement results for dispersions F1 to F8.

For dispersion F2, Pigment Blue 15:3 (copper phthalocyanine pigment;made by Clariant, Ltd.) was used as the pigment. The polymer wassynthesized in the same manner as the Production Example of dispersionF1, except changing the amount of urethane acrylate. The molecularweight dispersion (Mw/Mn) of the synthesized polymer was 3.0, and thestyrene-equivalent number average molecular weight was 5.62×10⁴. Also,the content of the urethane bonds, urea bonds, allophanate bonds, andbiuret bonds at this point was 0.8 mmol/g.

For dispersion F3, Pigment Red 122 (dimethylquinacridone pigment; madeby Clariant, Ltd.) was used as the pigment. The polymer was synthesizedin the same manner as the Production Example of dispersion F1, exceptchanging the amount of urethane acrylate. The molecular weightdispersion (Mw/Mn) of the synthesized polymer was 3.0, and thestyrene-equivalent number average molecular weight was 5.96×10⁴. Also,the content of the urethane bonds, urea bonds, allophanate bonds, andbiuret bonds at this point was 1.2 mmol/g.

For dispersion F4, Pigment Yellow 180 (diketopyrrolopyrrole; made byClariant, Ltd.) was used as the pigment. The polymer was synthesized inthe same manner as the Production Example of dispersion F1, exceptchanging the amount of urethane acrylate. The molecular weightdispersion (Mw/Mn) of the synthesized polymer was 3.5, and thestyrene-equivalent number average molecular weight was 5.82×10⁴. Also,the content of the urethane bonds, urea bonds, allophanate bonds, andbiuret bonds at this point was 1.2 mmol/g.

For dispersion F5, the polymer was synthesized in the same manner as theProduction Example of dispersion F1, except using a mixture of 50%benzyl acrylate and 50% isobornyl acrylate in place of benzyl acrylate,using Leben C (made by Columbian Carbon Ltd.), which is a carbon black,in place of using Monarch 880 (made by Cabot Corp.), which is a carbonblack, and changing the amount of urethane acrylate. The molecularweight dispersion (Mw/Mn) of the synthesized polymer was 3.5, and thestyrene-equivalent number average molecular weight was 7.35×10⁴. Also,the content of the urethane bonds, urea bonds, allophanate bonds, andbiuret bonds at this point was 1.0 mmol/g.

For dispersion F6, Pigment Blue 15:3 (copper phthalocyanine pigment;made by Clariant, Ltd.) was used as the pigment. The polymer wassynthesized in the same manner as the Production Example of dispersionF1, except changing the amount of urethane acrylate. The molecularweight dispersion (Mw/Mn) of the synthesized polymer was 3.0, and thestyrene-equivalent number average molecular weight was 7.58×10⁴. Also,the content of the urethane bonds, urea bonds, allophanate bonds, andbiuret bonds at this point was 0.9 mmol/g.

For dispersion F7, Pigment Red 122 (dimethylquinacridone pigment; madeby Clariant, Ltd.) was used as the pigment. The polymer was synthesizedin the same manner as the Production Example of dispersion F5, exceptchanging the amount of urethane acrylate. The molecular weightdispersion (Mw/Mn) of the synthesized polymer was 3.0, and thestyrene-equivalent number average molecular weight was 4.24×10⁴. Also,the content of the urethane bonds, urea bonds, allophanate bonds, andbiuret bonds at this point was 1.2 mmol/g.

For dispersion F8, Pigment Yellow 180 (diketopyrrolopyrrole; made byClariant, Ltd.) was used as the pigment. The polymer was synthesized inthe same manner as the Production Example of dispersion F5, exceptchanging the amount of urethane acrylate. The molecular weightdispersion (Mw/Mn) of the synthesized polymer was 3.5, and thestyrene-equivalent number average molecular weight was 6.13×10⁴. Also,the content of the urethane bonds, urea bonds, allophanate bonds, andbiuret bonds at this point was 1.3 mmol/g.

TABLE 29 Compositions of the dispersions Dispersion DispersionDispersion Dispersion Dispersion Dispersion Dispersion Dispersion F1 F2F3 F4 F5 F6 F7 F8 Benzyl acrylate 20 20 20 20 10 10 10 10 Isobornylacrylate — — — — 10 10 10 10 2-ethylhexyl acrylate 15 15 15 15 15 15 1515 Butyl acrylate 15 15 15 15 15 15 15 15 Lauryl acrylate 10 10 10 10 1010 10 10 Acrylic acid  2  2  2  2  2  2  2  2 Benzyl acrylate 50 50 5050 25 25 25 25 Isobornyl acrylate — — — — 25 25 25 25 2-ethylhexylacrylate 15 15 15 15 15 15 15 15 Acrylic acid 15 15 15 15 15 15 15 15Urethane acrylate CN961 50  50*  50*  50*  50*  50*  50*  50* Numberaverage molecular    5.23    5.62    5.96    5.82    7.35    7.58   4.24    6.13 weight × 10⁴ Dispersion Mw/Mn   3.1  3  3   3.5   3.5  3 3   3.5 Amount of urethane bonds  1   0.8   1.2   1.2  1   0.9   1.2  1.3 50*: The added amount was varied by a small amount.

(Preparation of Ink Jet Inks)

Examples of compositions that are favorable as ink jet recording ink areindicated in Table 30 as specific examples of aqueous ink. In Table 30,the added amount of dispersion is indicated with the amount thereof(solids concentration: total amount of pigment and dispersion polymer)converted to weight. 0.05% Topside 240 (made by Permachem Asia Ltd.) inion-exchanged water for prevention of corrosion of ink, 0.02%benzotriazole in ion-exchanged water for prevention of corrosion of inkjet head parts, and 0.04% EDTA (ethylenediamine tetraacetic acid) 2Nasalt in ion-exchanged water for reducing the effects of metal ions inthe ink system were used in the residual quantity of water in Table 30.Based on the compositions of Table 2, the ink jet inks of ProductionExamples F1 to F8 were prepared from dispersions F1 to F8, respectively.

TABLE 30 Ink compositions Ink F1 F2 F3 F4 F5 F6 F7 F8 Dispersion F1 7.5— — — — — — — Dispersion F2 — 4 — — — — — — Dispersion F3 — — 6.5 — — —— — Dispersion F4 — — — 6 — — — Dispersion F5 — — — — 8 — — — DispersionF6 — — — — — 5 — — Dispersion F7 — — — — — — 6 — Dispersion F8 — — — — —— — 8 TEGmBE 2 1 1 1 2 1 1 1 1,2-hexanediol 3 4 4 4 3 4 4 4 Glycerin 1015 10 10 10 13 10 7 Trimethylolpropane 4 7 5 5 4 7 5 5 Surfynol 104 0.10.1 0.1 0.1 0.1 0.1 0.1 0.1 Ion-exchanged water Residual ResidualResidual Residual Residual Residual Residual Residual quantity quantityquantity quantity quantity quantity quantity quantity TEGmBE:triethylene glycol monobutyl ether

(Evaluation of Ink Jet Inks)

(1) The Urethane Bonds, Urea Bonds, Allophanate Bonds, and Biuret Bondsof a Polymer and Dispersion Stability and Fixing Property

Dispersion stability and fixing property on specialized paper weremeasured for Production Examples F1 to F8 and Production Examples FA1 toFA20. Production Examples FA1 to FA2 were prepared in the sameprocedures as those of the Production Example of dispersion F1, esceptusing separately synthesized acrylates, containing urethane bonds, ureabonds, allophanate bonds, and biuret bonds, in place of the urethaneacrylate used in dispersion F1, to synthesize polymers that arevariously differed in the amounts of the abovementioned bonds, based onthe composition of Production Example F1 shown in Table 30. With theseProduction Examples, dispersion stability and fixing property onspecialized paper were evaluated. Measurements concerning dispersionstability and fixing property were made as follows. The results areshown in Table 31.

(Evaluation of Dispersion Stability)

The percentage change in viscosity (%) upon leaving each ink at 60° C.for 30 days was measured as an index of dispersion stability. A smallerpercentage change in viscosity indicates higher stability. For thepercentage change in viscosity, viscosity values were measured at anangle of 60° using the AMVn, made by Anton Paar GmbH, and 1−(value after30 days)/(initial value) was indicated in the form of percentage (%).

(Evaluation of Fixing Property on Specialized Paper)

The fixing property was evaluated using specialized paper (PM photopaper, made by Seiko Epson Co., Ltd.) and observing the rubbing off ofink when a printed surface and a rear surface are overlapped with a loadof 300 g and moved at a speed of 30 cm/s. AA is used to indicate thatthere was no rub-off whatsoever even after two times of movement, A isused to indicate that though there was no rub-off whatsoever even afterone time of movement, slight rub-off occurred after two times ofmovement, B is used to indicate that there was slight rub-off, C is usedto indicate that there was rub-off and transfer onto the rear surface,and D is used to indicate that there was considerable rub-off andtransfer onto the rear surface.

TABLE 31 Various bond amounts and dispersion stability and fixingproperty on specialized paper Fixing Dispersion stability property onUrethane Urea Allophanate Biuret (percentage change specialized Inkmmol/g mmol/g mmol/g mmol/g in viscosity (%)) paper F1 1.0 0.0 0 0 0.01A F2 0.8 0.0 0 0 0.1 A F3 1.2 0.0 0 0 0.05 A F4 1.2 0.0 0 0 0.1 A F5 1.00.0 0 0 0.1 A F6 0.9 0.0 0 0 0.05 A F7 1.2 0.0 0 0 0.05 A F8 1.3 0.0 0 00.1 A FA1 0.1 0.0 0 0 0.1 A FA2 0.1 0.1 0 0 0.1 A FA3 0.5 0.0 0.1 0 0.2A FA4 0.3 0.2 0 0.1 0.1 A FA5 10.0 0.0 0 0 0.1 A FA6 1.0 0.1 0 0 0.3 AFA7 0.5 0.0 0.1 0 0.2 A FA8 0.5 0.1 0 0.05 0.1 A FA9 2.0 0.0 1 0 1.4N.T. FA10 2.0 0.0 0.5 0 1 N.T. FA11 1.0 2.0 0.5 0.5 1.5 N.T. FA12 0.09 00 0 1 B FA13 0.05 0.02 0 0 0.2 C FA14 0.05 0.02 0 0.01 1 C FA15 10.1 0 00 35 A FA16 5.0 3.0 2 1 86 A FA17 5.0 5.0 0 0.5 103 A FA18 2.0 0.0 1.1 0250 N.T. FA19 2.0 1.0 1 0.1 231 N.T. FA20 1.0 2.0 0.1 1 351 N.T. N.T.:Not Tested

Production Examples F1 to F8 contain just urethane bonds and do notcontain urea bonds, allophanate bonds, nor biuret bonds. As shown inTable 31, these Production Examples F1 to F8 exhibit high dispersionstability with a total amount of the four types of bonds (practicallythe amount of urethane bonds) being no less than 0.8 mmol/g and no morethan 1.3 mmol/g. These also exhibited good fixing properties onspecialized paper.

Also in regard to the dispersion stability of FA1 to FA20 in relation tothe amount of allophanate bonds and biuret bonds, whereas fairly gooddispersion stability is exhibited with a bond amount of no more than 1.0mmol/g, extremely poor dispersion stability is exhibited when 1.0 mmol/gis exceeded. Meanwhile, in regard to the total amount of urethane bonds,urea bonds, allophanate bonds, and biuret bonds, excellent dispersionstability is exhibited at no more than 10.0 mmol/g and the dispersionstability degrades clearly when 10.0 mmol/g is exceeded. From the above,it is clear that the total amount of allophanate bonds and biuret bondsis preferably no more than 1.0 mmol/g and the total amount of urethanebonds, urea bonds, allophanate bonds, and biuret bonds is preferably nomore than 10.0 mmol/g. Also from the results of Production Examples F1to F8 and Production Examples FA1 to FA11, it is clear that the totalamount of allophanate bonds and biuret bonds is preferably no more than0.1 mmol/g.

In regard to the fixing properties on specialized paper of FA1 to FA8and FA12 to FA17 in relation to the four types of bonds and biuretbonds, whereas the fixing property is high when the total amount of thefour bonds is high and good fixing property is secured when this amountis no less than 0.1 mmol/g, the fixing property degrades significantlyat less than 0.1 mmol/g.

(2) Styrene-Equivalent Number Average Molecular Weight of a Polymer andDispersion Stability

A plurality of polymers, which are differed in styrene-equivalent numberaverage molecular weight and dispersion Mw/Mn, were synthesized bydiffering the synthesis time and amount of radical polymerizationinitiator, and by using one type or combining two or more types of thesepolymers and making the particle diameters of pigment-enclosingparticles differ in performing mixing based on the composition of theink of Production Example F1 of Table 30, Production Examples FB1 toFB15 of 15 subtypes of ink, with which various molecular weights anddispersions and various particle diameters are combined, were prepared.The percentage change in viscosity was measured for each of theseProduction Examples FB1 to FB15 of subtype inks of ink 1 and ProductionExamples F2 to F8. The results are shown below. The molecular weightsshown in Table 32 are styrene-equivalent number average molecularweights. The particle diameters of the polymer-coated pigment particlesin the respective inks were measured using the Zetasizer 3000HS (made byMalvern Instruments, Inc. (UK)).

TABLE 32 Number average molecular weight, dispersion, and particlediameter and dispersion stability Number average Particle Dispersionstability molecular diameter (percentage change Ink weight × 10⁴ Mw/MN(nm) in viscosity (%)) F1 FB1 0.51 3.1 100 40 FB2 1.12 3.1 100 20.1 FB33.1 3.1 100 0.2 FB4 5.23 3.1 100 0.2 FB5 10.21 1.3 100 20 FB6 10.21 2.2100 1 FB7 10.21 3.1 100 0.01 FB8 10.21 3.1 15 132 FB9 10.21 3.2 20 50.1FB10 10.21 5.3 300 80.5 FB11 10.21 10.5 100 1 FB12 10.21 11.3 100 20FB13 20.13 3.1 100 240.4 FB14 25.2 3.1 100 350.5 FB15 30.11 3.1 100 810F2 5.62 3 90 0.01 F3 5.96 3 95 0.1 F4 5.82 3.5 100 0.05 F5 7.35 3.5 1000.1 F6 7.58 3 90 0.1 F7 4.24 3 95 0.05 F8 6.13 3.5 100 0.05

It is clear from Table 32 that good dispersion stability will beexhibited when the number average molecular weight of the polymer iswithin the range of no less than 2×10⁴, and no more than 10×10⁴ and gooddispersion stability will be exhibited when the dispersion is within therange of no less than 2.0 and no more than 10.5. It is also clear thatthe number average molecular weight is preferably no less than 3×10⁴ andthe dispersion is more preferably no less than 3.0 and no more than 4.0.

(3) Evaluation of Fixing Property and OD on Specialized Paper

The conditions for polymer polymerization (synthesis time and amount ofradical polymerization initiator) in the production of dispersion F1were adjusted to synthesize 6 types of polymers that differ in numberaverage molecular weight and prepare various dispersions, and ProductionExamples FC1 to FC6 of inks were prepared based on the composition ofProduction Example F1 shown in Table 30. These Production Examples FC1to FC6 were subject to measurements of fixing property and OD onspecialized paper. Also, except using styrene in place of urethaneacrylate in the Production Example of dispersion F1, the same proceduresas those of the production of dispersion F1 were carried out tosynthesize 6 types of polymers that differ in number average molecularweight and prepare various dispersions to thereby prepare ProductionExamples FD1 to FD6 of inks based on the composition of ProductionExample F1 of Table 30. These Production Examples were subject to themeasurement of fixing property and OD on specialized paper. The ODvalues were measured as described below. The results are shown in Table33.

(Measurement of OD)

L*, a*, and b* were measured using the Gretag Macbeth Spectroscan SPM-50(made by Gretag Corp.) and OD value was calculated as the scalar valueof these measured values.

TABLE 33 OD and fixing property on specialized paper FC1 FC2 FC3 FC4 FC5FC6 Number average molecular weight × 10⁴ 0.52 3.21 5.41 11.01 19.3332.68 OD 1.8 2.2 2.5 2.6 2.3 2 Fixing property on specialized B A AA AAAA B paper FD1 FD2 FD3 FD4 FD5 FD6 Number average molecular weight × 10⁴0.55 3.1 5.23 10.21 20.13 30.11 OD 1.7 2.1 2.3 2.5 2.4 1.9 Fixingproperty on specialized C B A A A C paper

As shown in Table 33, with Production Examples FC1 to FC6, the fixingproperty and OD on specialized paper were both good when the numberaverage molecular weight was in the range of no less than 2×10⁴ and nomore than 20×10⁴. Meanwhile, with Production Examples FD1 to FD6, whichuse styrene, though a favorable OD is obtained when the number averagemolecular weight was in the range of no less than 5×10⁴ and no more than20×10⁴, the fixing property on specialized paper was poor in comparisonto FC1 to FC6. It is thus clear that aromatic vinyl monomers, such asstyrene, lower the fixing property.

Each Disclosure of Japanese Patent Application No. 2003-103473 (filed onApr. 7, 2003), Japanese Patent Applications No. 2003-173345 (filed onJun. 18, 2003), No. 2003-359294 (filed on Oct. 20, 2003), No.2004-023934 (filed on Jan. 30, 2004), No. 2004-036268 (filed on Feb. 13,2004), No. 2004-048025 (filed on Feb. 24, 2004), and No. 2004-111115(filed on Apr. 5, 2004), each of which is including specification,drawings, and claims are incorporated herein by reference in theirentirety.

1. An aqueous ink composition comprising: a pigment, having a particlediameter as determined by the light scattering method of no less than 20nm and no more than 200 nm; and a water dispersible polymer, having astyrene-equivalent number average molecular weight as determined by gelpermeation chromatography of no less than 5000 and no more than 200000;a 1,2-alkyldiol, having 5 to 8 carbons; and a monoalkyl ether, with 4 to10 carbons of an alkylene glycol having no more than 10 repeating units.2. An aqueous ink composition according to claim 1, wherein the1,2-alkyldiol is 1,2-hexanediol and the alkylene glycol monoalkyl etheris di(tri)ethylene glycol monobutyl ether.
 3. An aqueous ink compositionaccording to claim 1, wherein said water dispersible polymer comprises acarboxylic-group-containing monomer, an acrylate monomer, and/ormethacrylate monomer, wherein said monomers comprise benzyl acrylateand/or benzyl methacrylate monomers at an amount of no less than 40weight % and no more than 80 weight % of the total monomer weight,
 4. Anaqueous ink composition according to claim 3, wherein said monomers, inaddition to the benzyl monomers, comprise acrylic acid and methacrylicacid monomers.
 5. An aqueous ink composition according to claim 1,wherein said pigment includes a polymer-coated pigment that is coatedwith said water dispersible polymer.
 6. An aqueous ink compositionaccording to claim 1, wherein said water dispersible polymer containssulfur (S) at an amount of no less than 1 weight % and no more than 20weight % of the total weight of said polymer.
 7. An aqueous inkcomposition according to claim 1, wherein said water dispersible polymercontaining a urethane acrylate and/or a urethane methacrylate, the totalamount of allophanate bonds and biuret bonds with respect to the polymersolids is no more than 1.0 mmol/g, and the total amount of urethanebonds, urea bonds, allophanate bonds, and biuret bonds with respect tothe polymer solids is no more than 10.0 rnmol/g.